You have been very much misled. The game is MEANT to be solo play. It’s a SOLO game. The entire game is balanced around you NEVER TRADING. It’s a solo game that tacked on multiplayer and trading, and didn’t at all balance around those.
So you leveled a character, that, WHEN you got to end game, would take some farming before you were doing really great. The character wasn’t wasted, it was just going to be time consuming.
Fighting Nemesis bosses is MEANT to be hard, nigh on undoable, for some builds, until you get really, really good gear. They’re called Ultra Bosses for a reason. If you could kill them with just anything you picked up, they’d be pushovers, and some still ARE pushovers. If your build can’t kill nemesis, that doesn’t make it some awful failure, it just means you need to farm more for gear. If you didn’t want to farm more for gear, then someone should have politely steered you away from this genre, where the entire point is farming for gear and making new builds.
You can play almost anything without having the gear at the start of it, though. It’ll be better WITH the gear, and you might need to swap some skill points around…But it almost all works. The very few things that do not work without gear are things built specifically around conversion items, and those specific builds all have variants that function without the conversion items, and can be respecced later if/when you get them.
So when people say, adapt to the changes…You CAN. Because you’ve never actually needed the gear. This game takes time, and effort, and some base knowledge. The third, read up on the wiki and forums and you’ll be fine. Time and effort, that’s up to you to put in. If you don’t want to, fine…But that’s not really the game’s fault, now is it?
If you’d like to skip past farming, there are various tools to use, notably GDSidekick, to skip past loot farming and just get the epics and legendaries you want. I’m told there’s various hex editors as well to generate items, if you need a rare and don’t want to farm for it.
So you have many ways to adapt, if you choose to do so. If you don’t, well, that’s your choice.