Oddly enough after a long break I just popped in WoW lately to see what the game is now. Sorry to disappoint you but Legion is the same as everything before it. If you have even half a brain, you cannot die questing or doing solo content. And with the expansion coming to a close heroics are the easiest they have ever been in the history of the game. You can literally pull the entire instance and AOE everything down. Normal and heroic dungeons are obsolete and I don't know anyone who does them. Everyone only does mythic+ dungeons, which are the only thing challenging (outside HC raiding) at keystone level 10 upwards, depending on your gear and group. LFR raiding is the same tourist mode as ever, you can go in and not even press any buttons besides moving and you're set to win, champion.
If you do not enjoy the lore, storylines, leveling and trying out alts, and you are looking for a challenge.. well your only option at the endgame is finding a guild and start doing proper raiding. There is one more raid coming out before the next expansion. Mythic+ dungeons get so old so fast that you'll be sick of them in a week or two. They alone aren't enough content to make a player stick at the endgame.
If you do enjoy the lore, storylines and playing alts, well congratulations, there has never been more content for you than now. Every class has their own unique storylines and order halls and both factions have their own stuff going on. There just won't be any challenge to it. But there is so much of this pure time wasting content that you'll be set for months and months.