Wrex's attitude in the first game cannot be only explained with bitterness. You'll learn from him that he performed contract kills on businessmen in Noveria, was piracing (for Saren) and even wanted to kill a friend for credits. There's not a bit of bitterness in his words when he talks about the thing with Aleena, it sounds like it was an adventure for him. He was sizing up everyone for a fight (elevator). His first reaction to conflicts was always violence and intimidation (Virmire, Rachni Queen). You could see that his whole nature was inherently violent and ruthless and because of that he was the prime example why Krogans were considered dangerous. (And this also made the character more interesting). Yet what was it how he was called in the 3rd game? An anomaly? And I'm supposed to forget all these things. This is why i liked the Genophage arc much more with Wreav. With him you don't get these nonsense lines like "hire him a food taster" or "the other Krogans aren't like you Wrex".
Even in ME3 that "anomaly" talk didn't quite work. The only reason he was the biggest leader of the Krogan was because he was good at their war games. He could only get into his position by being as vicious and brutal as the rest of them, and it's not like he ever seemed sorry to have to do it (nor should he be imo, that's who he and the Krogan are, his character should stay true to that). He was still somewhat violent and impulsive, like with his arrival on Sur'Kesh and the way he was laughing when Wreav got eaten, if I remember that scene quite right. But for whatever reason ME2 and 3 just treated Wrex's violence more lightly, kind of comically. Like, "That's our Wrex!" which got kind of irritating.
Eve is a little annoying for similar reasons. We're supposed to believe that female Krogan don't want wars and they love all their children and why can't the world be run by women blah blah (IRL women may well run the world better than us men, but in this context it was annoying). There have been female warlords, and Krogan mothers have been letting their pups or whatever they're called kill each other in the nest so the strongest survive, to grow up and go off killing each other on the battlefield. But all of a sudden they aren't like the males.
It was kind of silly that the Genophage arc sold you the idea that Wrex and Eve alone could make that much of a difference to Krogan attitudes. I get that the devs had to make curing the Genophage a viable option, but even so, if you think about it the Krogan are going to do whatever they're going to do regardless of who's leading. And like you said, I get the feeling that a Wreav playthrough allows you to view it more realistically without the rose tinted view of Wrex. I always liked Wrex in general, but his portrayal in 3 definitely felt kind of off.