My biggest issue with PoE is that you need to plan out your build from the start since you can't really respec. In that way, I find the experience more dynamic in D3 as you can adjust your build as you find cool items.
That said, D3 does lack some depth, while PoE is probably too complex now as it expanded over the years.
The 2 games have different audience though as mentioned. D3 is more casual and PoE more hardcore, that's good that both playerbase have a game for them.
I don't have much faith left in Blizzard though, I think most of the talent left years ago. Maybe they'll surprise me, but Diablo IV isn't something I have huge interest in, maybe closer to release in 10 years.
Blizzard also needs to up their development rate, and especially making content updates. Their glacial pace isn't working today with so much competition in all genres.