They do different things for me.

PoE satisfies my creative side in the sense that I can find say, a great unique item, or support gem, want to make a cool build out of it, and give that a shot. I also love that the endgame experience is highly customizable (in the form of hideout, as well as map-running choices, atlas passives, etc)

I'm only level ~40 or so in D4 so take this with a grain of salt -- although D4 doesn't appear to have nearly the same level of customizability that PoE does, what it does offer me is an enormous world I can explore pretty much from the get-go. PoE is extremely linear, all throughout. Another thing D4 does really well is the feeling of its combat. Basic skills being a free, but weaker skill to help generate resource to more infrequently use a Core skill is a satisfying recipe, IMO. PoE would often feel like a screen clearing stomp-fest (and, at times, require it) and even though that can be satisfying in its own way, it's more fun for me if I feel like I have to struggle and claw my way into wins.