Btw why do people want I-frames? Isn't that just an easy out with dodging etc. Take less damage might be a compromise but not invulnerability per se.
I don't know if majority of the people who disliked Geralt's evades were thinking in technical terms like that. It's just that if you play a lot of other action games, Geralt will feel like he's getting hit where other action heroes would make it through unscathed.
The thing is when you're in a game dealing with multiple aggressors, it's realistic to be hit if you're within range of any of them, but that usually doesn't make for a fun game, so a dodge with a specific period of i-frames rewards the player for dodging at the right time and keeps them in the action. And I think CDPR wanted it to feel a certain way.
To use an example you might have seen. In Dark Souls after you successfully parry and riposte, once you're in the riposte animation, the entire sequence has i-frames. Realistically it doesn't make sense that enemies can't hit you while you're skewering one of them, but just imagine only being able to riposte when it's 1v1?