It's pretty bad, true. They keep reducing the number of questing zones each expansion, really puts a damper on enjoying alts. Both in bfa and legion you pretty much do all the quests on your first trip to max level, leaving alts to repeat the same shit. Sure, heirlooms help, but I do miss the days of LK and pandaria, when even on your third char you still had areas you never quested in. Islands were fun for one or two alts, but after that they become soulcushingly boring. And I'm still annoyed that they axed invasions. At least in legion you could work on a few alts at the same time, now you get an extra timer egging you on. I like to take my time, do a bit of leveling, tab out and watch some youtube, just to break up the monotony. Does not work when you have to make up for lower invasion XP with that shitty bonus xp buff.
Maybe it's time activision took a look at leveling process. It worked fine in the past, but it's been 15 years, maybe it's time for a new take on it.