Early game they are pretty much the same. It's later where they formerly dealt pitiful damage that they change (at level 10 they get 3AP shoot which obviously makes a very big difference). They're still no Champions, and overall I still like Arcanists and Sages better so Champion-Champion-Sage-Arcanist is probably still the optimal comp, but they can one-shot most things which means their versatility (i.e. their range) is actually relevant. It becomes even more relevant due to the AP nerfs meaning Champions and Vanguards can't just one-pop the entire encounter before it begins on Very Hard. Sir Geraint with his mobility buff (again, much more important on champions and vanguards now due to lack of AP generation) might be a contender for my best hero out of the roster. He slaps, buffs and CCs. Balan (his new kit is fucking amazing) and Lancelot are probably still better on my Old Faith Righteous run, but Geraint is very, very good. Bors just deals a fuckton of damage.
Defender is basically the only class that wasn't improved much by 2.0. Playing with one after the early game is a band-aid for poor play. They're not useless (as marksmen were before the patch), they're just clearly the worst choice to bring on a mission (if you're a decent player - if you're not, their ability to tank hits is more relevant) as they're the only class that can't contribute to ending encounters faster meaning the risk of vitality and injury damage grows. I really enjoy encounters lasting longer and Vit+injuries being more relevant, so I often bring one anyway.
All in all, I'm definitely not saying Marksmen are now optimal - I'm saying that you don't feel like you have an empty slot if you bring them on a mission. They definitely contribute. Overall I feel like 2.0 improved so many things, class balance and combat being the main one. The fact that I no longer feel as punished bringing the worse classes and that none of my champions can just outright one-shot big encounters (even if Balan can come close with his YUEG AoE kit) is a pretty big improvement.