Used to be that during an attack animation there was a very specific time frame when you could interrupt the attack animation and dodge away. In other words, it was an intended (somewhat limited) way to get out of the animation, unlike weapon swapping.I admit, I haven’t been testing this very thoroughly recently to see when you can or can’t roll in the middle of attacking.
There definitely seems to be a pause after the katana dash attack where your character is just standing there posing dramatically, so if your target didn’t die, they get a free swing or two at your exposed back.
And yes, the reason why I never got into using e.g. hammers was the fact that once you start swinging it, you expose yourself to attacks, so you’re right that if you couldn’t interrupt the attack animation by rolling at any point, people would probably gravitate towards weapons with the fastest individual attacks. I certainly would.