Both have their pros and cons. Path of Exile I feel has the better endgame gameplay loop. You are grinding, yes, but you are also advancing your Atlas towards a goal. MXL has more challenge though, and tackles bosses better I would say. In PoE, bossing costs money [for economy balance reasons], which I feel is the wrong way to go about it. Bosses [and their drops] should be gated by how hard they are, not by how expensive it is to buy a set to run them. From my experience, it is always more lucrative to sell a boss set, than run a boss, in Path of Exile. Unless you're bossing 24/7, which MAY edge things out in your favor in the long run.
That's why, despite having the better gameplay loop, PoE still kind of falls short and MXL edges it out. When I'm done gearing a character, I would have to grind more to tackle end game bosses? After grinding for tens of hours to gear my character with some decent to good gear, the last thing I want is to grind to buy boss sets. I'd rather grind towards my next build instead. Which is always what happens with me.
One thing that the recent Harvest League has improved is the addition of deterministic crafting. Now it feels worth it to craft your stuff, whereas it used to be that it was often cheaper and more reliable to just buy the item you needed, instead of crafting. Why spend currency crafting when I could just use that currency and buy the item outright, instead of gambling? Well, Harvest League fixed that. Who knows if it'll go core though. Until this league, MXL was the clear winner in crafting because it never felt like a waste of time and currency.