PvE in like, every MMO nowadays is all about straight forward optimization. No one has build variance anymore. Not in hardcore scenes, at least. There's one path, we all follow it because it's the good path. So I've got nothing for you there. Cookie cutter is the way to go. B&S in particular turned out this way because it was designed so every attack is avoidable. If you never have to get hit why in the world would you build for defense? It just slows stuff down. You rely on stats for damage, skills for defense.
PvP is where you want to be if you're looking to utilize the combat to its full potential. Gear doesn't matter in PvP so skill choice is all you have enough Blade-Soul Gold. Every match varies so there wont be a catchall build for you to use. I don't PvP so I'm not speaking from experience but I think I've got a good handle on it.
I very strongly dislike many things helltrash said."cookie cutter is the way to go" "we all follow one path beacuse its the good path". These kind of additudes are probably what upsets me most about gaming in general. When did gaming stop being about having fun and start being about becoming the next pro e-sports player? "I cant play this class beacuse its not viable" "I cant get this skill cuz this one is better" Why dont people stop thinking about what follows the meta or whatever and just do what they want? Its a dam video game, have fun with it
The best way is to check the class specific forums, and check the pve build guides for the classes. Most guides will list 1 or 2 popular builds, often with the caveat that certain builds aren't efficient until 50, or require certain hongmoon books to be viable. Look for the classes that have more than 1 viable build.
For example, assassins have a lightning build (stealth based) and a dark build (out of stealth), but the dark build isn't really effective atm because of missing hongmoon skills with . At 50, both builds should be perfectly viable, and are both different play styles.
Warlocks have 2 or 3 builds (ice build, dark build, dark/ice build), force masters have fire build vs ice build, etc.
In terms of gear, yeah, that's pretty set unfortunately, although there are elemental accessories that you may swap based on your build.