Remarkable 2 is better, because of the features it doesn't have. The best feature of Remarkable 2 is how quiet it is, it doesn't do anything except for Book reading and note taking. No notifications, no messaging, no email, quiet tech.
Has PDF annotation improved on Remarkable 2? Otherwise it's trival to disable notifications, messaging, email etc (at least on Boox and there are quite good youtube tutorials about how to do this), so that's not a particularly strong differentiation. "You can have any color you want as long as it's black" only works as a selling point if other cars can't be black.
It's like how my screwdriver is significantly better at driving screws than my swiss army knife. Purposeful design drives a better experience