Make your mind up man, an alt run isn't a carry, because virtually everyone will need gear and that means having a minimum level of gear, and most guilds didn't want people to change classes, especially if they'd already been raiding with them and got a bunch of gear. If they did want them to change, yeah then they might bring you to an actual carry, but yeah that was a privilege not everyone got access to. It's also something you can still access today with the right guild.
What exactly are these "mandatory grinds" you're claiming the game is unplayable without? AP? Is that it? Because it sounded like it was a larger complaint. And the problems with that peaked in early Legion. BfA hasn't been nearly as bad, and SL looks to be less bad still.