Without Atlantis DLC, you may be stuck at 32 points mastery max. Try the below suggestion:

"If you right click Titan Quest from your games list and select properties, you can go into Betas tab and switch it to, "anniversary_ragnarok". It doesn't come with enhanced mode, but it allows paths to have 100 max on the paths bar."

(Credit to: Cogs, Spigots and Oddity Fuzz)