I have the same issue.
Yesterday I hit Level 132 and my XP Point go minus. I play a NG+ and have all skills maxed out, with about 15 Skillpoint left to spend.
I play on Insane difficulty but have to say, it really doable. Yes it is tough but I have not yet experienced any foe I could not defeat (beat all architects).
I hope this does not Change now. I only have the main misisons left to play to get my "Insane-Playthru" Acchievement.