I know neither of us knows for certain, but I'm pretty sure they won't prevent you doing other stories once you hit 50. It just won't level you past there. Thus you only need to level 8 characters to see all the content if you refuse to do content unless you're getting XP.
Also, let's be real - half the players in WoW currently haven't seen entire expansions, or large fractions of expansions. I've played since literally beta of Vanilla (open beta), and there are zones and sides I've still never done - especially in Cataclysm and MoP. And right now I just level by dungeons because zone-leveling is such a shitshow. And I know many new players do too. Further, you'd need at least 4-5 characters to see it now even with the same strategy (i.e. only do zones whilst they give you XP), given how few zones you need to do before stuff goes grey. We can do that math together if you really like but even optimizing to follow different routes each time it's going to be at least 4 characters, and I suspect 5 or 6. So that going to 8 is a problem? Come off it. If anything it being neatened up will help. 8 characters doesn't even fill one server. I mean, how many have you leveled to max level for an expansion? It's at least 30 for me, probably more, over 15 years.
I can't see it as making it worse. On the other hand I don't really object to removing it.
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You don't get weaker, dude. You stay the same, it's just now 120 is called 50. This is not rocket surgery.