Almost all the build guides for Sorcerer use every single skill from the defensive node. Stuff like that indicates a problem with the class to me when players are ignoring the majority of offensive options in favor of 4-5 buff options boosting a singular skill to crazy he's.
Additionally the impression I've gotten from other classes is that several have 1-2 builds that are significantly better than all other options. You can't get perfect balance, but the 'best' should ideally be only ~10% better instead of 40-50%
If I recall correctly that's how it's always been with Diablo. I've remembered each D3 season there was a different build for each class that would work really well. So while the content was always kinda the same, the game forced you to try other builds if you wanted to beat the highest difficulty level consistently.
Looking at how uniques work at the moment they always seem to affect skills directly, groups of skills, weapon types or damage types. So if you want a strong build you have to get uniques that stack well and buff the same kind of tools you want to use.
Logically you want to buff one damage skill to the extreme but since there sometimes are no overlaps and uniques are sometimes skill specific, you run into the issue, that a different damage skill just doesn't do much damage anymore. This concludes in you essentially having to use actives and passives from your ability tree that also buff your one "super-skill" or boost survivability. Since you're not restricted when it comes to buffs, the most logical choice is then to just fill all remaining slots with buffs or skills that activate buffing effects. Even mobility gets pushed out in high end builds for more damage.
I don't like it, but as soon as you make an effect that only works in one context, you have effectively ruined build variety because theorycrafters will just min-max the hell out of it. There probably is no good solution that helps build variety and at the same time makes uniques feel interesting and exciting. Because when everything is viable, unique effects will mostly just be stat boosts and thus boring.
If I recall correctly that’s how it’s always been with Diablo
So, I'll be a bit of greybeard here with a "Not ALWAYS!". But I'm being sorta pedantic in that...
Diablo 2 in version 1.09 and before were my favorite. The 1.10 patch was where Blizzard introduced "Synergies" to the skills as well as a boatload new Runewords (Enigma, Chains of Honor, etc.)
Prior to that, the balance wasn't perfect...but the "best" builds weren't stupidly above the rest, and everything sort of had weak points or blind spots. You could argue, and I'd agree, that the game perhaps didn't have as much content to explore at that point, but I enjoyed the game far more in that era than what came after.
In 1.09 you could feasibly do any build and still sort of enjoy the game. I had melee sorc builds, elemental paladins. My favorite PvP build was smite/FoH pally. But what came after? Hammerdins, Wind Druids, bonermancers galore. The game broke so many builds putting them miles above the rest. But instead of fixing that, blizzard leaned into it and released content that only very narrow builds could complete. Ubers? Without a smiter? Almost unheard of.
Itemization is also a big part of ruining that. I've always loved RPGs that have "Sets" and "Uniques" that are powerful, but the best is always a Rare (or equivalent such as crafted item). Sure the odds of godrolling the best items are astronomically small, but at least it lead to diversity. Everyone who just wants to play can equip the same gear as each other, but those who want to optimize need to work.