Once I got to level 11+ there were no challenging fights anymore. Even though I forced the "scaler" on in all areas. Even fights I remembered as being difficult in previous non-PotD playthroughs, like the lich and the adra dragon, were pretty easy (although those ones were not in upscaled areas). And I'm not even trying to get the best character builds and party composition.
While it is definitely true that Path of the Damned is too easy it isn't really for the reasons people think, not even Mr. Boeroer (of course this is a part of the reason)
It's your meta knowledge and your improved knowledge around the mechanics. Happens to all of us.
Try solo PoTD next!
During the early game PotD is somewhat challenging. For people who have a deep understanding of the game even still it isn't pushing them but you can't just faff about, you have to try. But then because the XP was never properly balanced you end up outleveling everything, leading to encounters turning into jokes where you steamroll everything.
One thing I have tried that helps is rolling with a smaller party, like only four party members. It helps bring more balance. Try leaving out your most effective companions, try no priest. It forces you to adapt somewhat.
They have said they will balance the XP much better in Deadfire to avoid this problem.