I agree for the most part, but the whole "Mac is worse than the plague" idea that pops up on this forum is just really unhelpful, even apart from being hysterical and grossly disproportionate.
Starting from a position akin to "any writer I don't like should be fired immediately" is exactly the kind of unreasonable, aggressive and hostile 'feedback' that they'll never listen to. It shuts down any potential for communication, which is probably why a writer hasn't appeared on the Bioware forums in literally years. It paints fans as shrill and delusional, while also ensuring that anything and everything they offer as feedback never gets to anyone who could do anything about it.
There are better ways to express what you want from future projects that don't involve personal attacks on devs, frankly. Suggesting that Mass Effect has an editor for the lore and continuity is a good start. I'd really, really like it if Mac could keep things consistent, and I'm still disappointed with what happened with ME3 and its aftermath, but it should be abundantly clear by now that sitting on a forum repeatedly attacking someone for two years is not going to get them to do anything differently.
Let me tell you, I do sincerely agree with your point here, and I say it with no ounce of remorse:
Mac Walters needs to be relieved of most, if not all, of his writing responsibilities on Mass Effect (I'm not saying to fire him from BW, though if he were, I can honestly say no tears would be lost from me.) I'm not saying that because I don't like the man. I'll be honest with you; I don't like Mac Walters. And I'm going to explain why.
First, I'll say that when I advocate Mac's dismissal, it's not out of my dislike for the man. It's because I legitimately believe that his presence and style of writing is a harmful influence on the growth and evolution of Mass Effect, both within the games, and with expanded universe material. He has displayed an alarming propensity to disregard some lore and canon to make what he wants a reality within the franchise. In essence, he's pulling the 'screw the lore, I'm the writer and I can do what I please' card too often. Now I'm not going to claim that this is a perpetual usage, or that every action of his is to make whatever he wants happen (which is true, it's just that he usually manages to stay within the lore when doing so). But he does it with enough frequency so as to make excuses for why he can do and have what he wants to have. I think that by far the most egregious offense of this was with the ending of Mass Effect 3. Regardless of ones opinion of the ending, the supposed information that Mac and Casey Hudson sequestered themselves from their fellow writers and wrote the ending that they personally wanted for Mass Effect 3 and didn't bother sharing it with their peers or having it evaluated or reviewed was absolutely unacceptable and unprofessional on their part, and, if true, should have led to some kind of reprimand from higher-ups about it. To that end, I'm willing to criticize both BW leadership and EA for not laying down the law or whatever on their employees for acting as such.
Next, I'm not going to say anything about their decision to not change the ending or anything, but I think a real lack of communication on the part of many, specifically Mac Walters, about the intent or ideal of what they imagined for the series is unhelpful, and more importantly, disturbing if this is par the course for them in the future. They seem to be going out of their way to not have to deal with any kind of hardball responses. Sure, they can easily come on here and look and see the feedback, or hear about it from community organizers, but I believe the purest, most raw and direct form of feedback is to indeed submit yourself to the fans. Believe it or not, most of us are willing to communicate with you on what we see as problems, and whether or not they are aware of them, or they wish to address them to the community. Mac has really shown a major reluctance to do so, at least on a level that I believe to be real.
Personally, I'm the kind of guy who doesn't like to see bias in feedback, and I have a feeling that its been skewed in Mac's favor by Mac himself. I want to hear opinions that are telling me that I sucked at what I did. And believe me, you can tell a person they sucked without being a complete jerk-ass about it. Being upfront and direct in telling someone that they sucked, and more appropriately, why they sucked is a big measure for getting to the core of a problem and fixing it. You don't have to call a persona a gay stupid **** who's a completely moron in the explanation. And I believe Mac is fundamentally antagonistic to that principle.
As demonstrated here and in other media, he has a tendency to create inconsistencies within the universe. I could understand if this was a second-party writer hired for the job, but he's the bloody highest ranking writer at present and he can't even keep the lore of the universe straight. Now whether this is by design or ineptitude or mistake is irrelevant. None of the conclusions presented (that I can personally observe) are appealing or good.
Next, he does have a tendency to inflect too much of his own preferences into a story, up to an including his views on certain characters and his own ideals into a story. Now I understand that writer bias is going to occur. I'm not here to talk about that, or why it's obvious Mac's views are going to be inflected into the tone of the universe or why. I'm saying that in game, that presentation shouldn't be the only one (since it is specifically an RP'ing game designed to allow the player to make a complex PC capable of having different views and opinions over most, if not all, of the important aspects and details related to the story and universe. This includes interaction with squadmates and player agency in the main PC. Now I'm not going to say that this was entirely Mac, but in ME3, we were treated to an awfully specific way for Shepard to interact with a certain female blue character that wasn't all that remarkably controllable by the player, no matter how they viewed her. Really, the only aspect of control over the relationship with said character that the player wielded was whether that relationship was platonic or romantic. And there were other instances where Shepard felt more of his own character. I'm not saying that that is inherently bad. But in Mass Effect (an aforementioned RPG), it is. Shepard was given too much of a development in ME3 to the detriment of the one thing that made him so fun to play as; the players ability to develop him (or her, sorry I'm going to be referring to Shepard as a male) to their own manner. And while there was still choices and such, they felt much more limited, with an often outright omission of characterizing views for Shepard. Yeah you could make paragon and renegade decisions, but they felt more like actions than actually establishing the views of a Shepard. They told you that you had to hate a certain Human-Survivalist Organization, even if you could be sympathetic and supportive of them in a previous game, and they didn't give you an opportunity to define why you had to hate them or despise them. They went ahead and told you that you were supposed to be morally and ethically outraged by them. Now I don't know how much of this is all Mac's fault, but as the head writer, he (along with Casey Hudson) bears the responsibility for this happening under their watch. And looking at what Mac seems to want to be doing, I think he had a fair hand in much of this. Now my argument isn't that I'm upset that Mac's views don't gel or mesh with my own opinions and views, it's that he's not leaving much room for anyone else with any different views.
Lastly, the general quality of the writing and storytelling itself is simply not very effective. The man does not know how to write a story or a universe on a macro-scale. He's simply not fit for the job. Mass Effect 3, contrary to a lot of even my own opinions, did a lot of things right. The problem was the execution. The concept might be sound, but when its lost in translation in the writing, it can be disastrous. It's the difference between a diamond and a piece of coal. They're the same thing fundamentally, but there's also lot of chemical and physical stuff about the mixture and the mass and whatnot (please excuse any scientific inaccuracies). One is beautiful, pretty, and useful, and the other is a diamond 
Now I'm not going to describe which is which for anybody here, or whether or not a view is objective or not (all of this certainly my opinion alone after all unless you choose otherwise). I'm going to say that from what I like to think of as a pretty fair and considerate if not unbiased perspective is that due to a combination of all of the above mentioned factors, I think Mac Walters is a terrible fit for writing in the Mass Effect universe, specifically the lead writing position.
When BW asks what is wrong with Mass Effect, I will be up front and honest with my opinion: Mac Walters is what's wrong with Mass Effect.