Go ahead some of us prefer it before, Nor was I stating that I think D2 or D3 even POE skilltree is the best. I just like What D2 did for options and viability. Short of this season I'm not a fan of eventually one meta builds on certain classes needed to progress.
What's laughable is you think some of us enjoy D3 now or should in that respect. I would also hope that D3 mechanics are much better than a game that came more towards the beginning of the last decade vs one that came out in the last 3 years that showed blizzard only marginally got what the game was about and how to evolve it.
How about the D3 mechanics are better than every other game in the genre, not just D2? But when you bring up D2 that's what I'm gonna compare it to (you did it, not me).
D2 didn't have 'options and viability' like you think, every game with builds has best builds, D2 was just a very easy game, that's the reason more builds were 'viable'. Imagine if the endgame in D3 was just doing the storyline on fucking Hell difficulty. Or Master under the new system. That's what D2 was like. Of course everything is viable then.
Path of Exile? The only reason it's not 'solved' constantly is because it's so convoluted and they patch often enough that it can't get stagnant. That's not great design either though, it just means that it's difficult to find the best builds due to obfuscation.
D3 has LOTS of 'viable' builds, you only have to go to specific ones if you're pushing like world top levels, and they're still different for solo/group/farming/etc. The harder you make the content, the more an optimal build is required. Not in D3, in any game. The fact that you think these other games don't encourage optimal builds has nothing to do with the skill systems, and everything to do with the lack of difficulty forcing you into them. For most people PoE is about doing hardcore leagues over and over and starting over constantly. In D3 it's more about pushing yourself at the highest end, not the early parts of the game.