I play Hearthstone a lot. The game looks great. Bugs exist but are rare and get fixed fairly fast. I've personally encountered only a few in the many years I've played Hearthstone; ofc they look many when there is a small industry of streamers whose work is to target big studio games and show every little bug (often coming from some obscure interaction) as if it is a catastrophe that will melt your PC. But hey, outrage sells.
D3 was largely abandoned more than a decade ago so I have no idea why you are comparing it with PoE. Necro and the 2-3 extra zones we got post launch were the second expac content that could be implemented and since then it's been operating on a skeleton crew. I would hope any game that is actively been developed can have more variety than a dead game.