Path of exile is absolutely better than Diablo 3 in every single area that counts.
To your question OP; Yes, D3 is finish the campaign, then do nearly the exact same content while slightly upping the difficulty by a few % (greater rifts).
Actually, if you want a quick rundown;
Farm one area until level 70 with massacre bonuses.
Craft armor and weapons because who needs to rely on item drops in an ARPG.
Immediately skip a couple of the 17 difficulties and put it on T1 because then sets can drop.
Now stand in town and do regular rifts or bounties.
Spend a couple hours at most doing the Season Journey and then get handed your 6p set.
Upgrade rare weapons that you craft and get your sets' mandatory unique weapon.
Now skip even more difficulty levels and move on to T6.
Now do greater rifts until you run out of stones, then do regular rifts.
And now, because a game that's supposed to be around hunting loot instead just hands you everything, the only thing of worth is trying for leaderboards. So get ready to use 1 set for your class that's far better than the others, and have no choice in items because there's multiple mandatory legendaries that your set requires.
But don't worry, having all the items drop all the time just means you get to hunt for the same pieces with just slightly higher stats!