Can't agree. Path of Exile's combat feels more robotic and stilted, and the mechanic I enjoyed the most early on was the gem/materia-type system and that just became tedious pretty quickly.
It has some good elements but didn't gel well.
I feel the exact opposite when comparing combat. Combat in PoE is smooth and fast, not as good as D3, but it moves. Grim Dawn can be slow and clunky... At least playing melee and firearm characters. I haven't messed more than a few hours with casters and summoners.
I also cleared all of Grim Dawn in about 2-3 days of playing (Didn't do much with factions but cleared the bosses and most side areas I could research). PoE has a bit more longevity for me.