looking up end game builds on YouTube yielded nothing but constant explosions and insta-dead mobs and I noped out.
That's a development of the last few years. Also flashy cosmetics.
Since there's a serious farming aspect to loot, clear speed has slowly become king, helped by a slow but steady power creep. It's the inevitable conclusion of this type of game: what kills more faster is inevitably highly prized. Characters are built around it, items are chosen for it. It's not my favorite way of playing, but I don't know if I'd go back to Diablo 1's slow and steady speed.
I must say that to get to that speed, you need to finish the campaign first; it's purely endgame. And to make a character that can do it, you need some solid character building and enabling items. Sure, you can copy-paste others' builds, but I feel that doing it yourself makes it satisfying. When I played, I played solo-self-found (no trading) so I had to earn each upgrade. There's a satisfaction when your build and items you've found combine to crush your enemies properly. Shattering a whole screen is fun when you get there, it's proof that your concept is effective.
All that's just useful for mobs, and doesn't do shit against bosses. You still need to strategize against bosses, evade hits, etc. The game is quite challenging if you don't take shortcuts, despite crushing mobs. And with the endgame map system, you can always challenge yourself further with higher level maps, and add effects on maps that make it more difficult but more rewarding. To me, anyways, it's always been about the challenge.
I haven't played in a couple of years though. Heard they were aiming to reduce the speed a bit in PoE 2.