It is important that one is a shooter though. The skill required to play it is less important because the action styles are just so different, thus the skills required to play it are different. Being good in a shooter is not going to make you good at TW3's combat and vice versa. In one your aiming a gun while ducking behind cover most of the time, occasionally tossing out a biotic. In the other, your swinging a sword while dodging and rolling between the enemies while using your potions, bombs and signs in a strategic manner. Action oriented or not, skill based or not, the styles are just way to different to make an accurate comparison.
Hmmm, methinks we're not gonna convince each other on this one. 
IMO, It wins because it's better. As it was pointed out in the other posts before this one, the swordplay is better, swords aren't treated as clubs you whack enemies with, and for all the reasons I stated before about the lack of movement. I don't think the DA team can't do it, they just won't do it. They seem quite content to just keep on simplifying their combat system. I get that you like it and think they should never change, but I would prefer they do.
Yes it does matter. As Wolven pointed out. Being good at one does not mean you'll be good at the other due to how different they are. I know people who are amazing at CoD then get their butts handed to them in something like Devil May Cry which is all swordplay. Sure there are some people who can play both very well, but not always. But yeah, we're just gonna have to agree to disagree.
Well, you mention simplification as a bad thing, but it seems to me like the endgame of simplification would be something more like the witcher. It's elegantly implemented, yes, but complicated it ain't. DAI still has limited tactics, it has various status ailments and cross class combo attacks to take advantage thereof, it has three distinct classes with nine distinct advance classes and many distinct subclasses. It's streamlined from its earlier iterations, sure, but it's anything but simplified. The witcher has five magic spells, a fast attack, a strong attack, and a single class. Yes, there's more to it, but not significantly more.
In any case, I wouldn't deny that they're different skill sets, but I think that's immaterial. What's important is the one-to-one relationship between a players input in real life versus the avatar's actions in the game, which is intrinsic to action gameplay, and which any given shooter has in common with the witcher and a million other games. This just isn't necessarily the case with DA and other games like it. I could have one arm with one finger, and I'd still be able to (literally) poke my way through DAI. I wouldn't be able to complete many shooters like that - or any of the witcher games, for that matter.
Thankfully, in my case, I have no disability preventing me from enjoying these games (and as I said, action games are my preference, if ever so slightly). But it's not something to discard lightly. Beyond that, the gameplay styles are just so different (not superior or inferior, just distinct), and plenty of people simply prefer party RPGs flat out. I can't imagine managing a party of companions with TW's system. It's wonderful when you're playing a single dude, and a single class, but I flat out don't think it's capable of managing a diverse group with that many skills.
We probably can't convince each other that the other is in the right, but I think what we can agree on is that TW3 is a gamechanger like Skyrim was a gamechanger. It's inevitably going to influence whatever Bioware comes up with next, and Bioware has a tendency to take precisely the wrong thing and run with it. I like fixed protagonists sometimes, and I like action games frequently but I feel very strongly that neither of those things should be Bioware's takeaway from the success of TW3 (which, if it's at all vague or unclear, I goddamn loved). I want them to know that the sentiment exists out here. Even if you prefer action games, there's still room for RTwP party based RPGs these days.