On max difficulty, I felt everything got way too easy by ~level 22--24 or so. I guess when you can craft your first enhanced Witcher set which, for me, was the Cat set. I love the light armor Cat skill attribute, but it probably needs some serious balancing.
Granted, things can still kill you rather easily if they hit you, but enough experience you learn how to not get hit, which is really the primary function of the combat system: 3 out of 4 standard "fight moves" is damage avoidance. So, that should tell you something.
So, it was both easy and still challenging enough for me to enjoy it, but I felt like I could still take on most things. Contracts ceased to be difficult. I no longer had to Yrden any kind of wraith or worry about oils and potions all that often, for example: I just swing and they die.
But, at that point, you do feel like you are going through the motions: clean up some side missions, clear some events, dabble with the main story or ignore it because you still don't want everything to end.
I estimate that the final 100 hours of my 200 hour playthrough, I was feeling like this is pretty much over, I'm just dragging things out. ...It's still fun though.