The full take is a lot more nuanced. Specifically:
The problem isn't that control spells ruin 5e, it's that they specifically ruin difficult encounters against one hard threat. And that Legendary Resistance is a bit of a kludge to make that not true.
And I'm fond of his more specific reactions, though I think they're maybe a little narrow. Like I've pointed out in other threads, D&D 5e has limited distinctions for encounters that are basically "resource attrition" and encounters that are meant to be more tactical showcases against powerful and deadly opponents.
Basically, "boss encounters" vs. "the dungeon itself is the boss, and this encounter is one of its attacks."
In the former, control spells are a problem that we need something like Legendary Resistance or these moves Mearls thought of here to solve for, since we WANT a multi-round conflict where most every hit or miss or resource expenditure matters. In the latter, control spells are just another way to mitigate damage and take out what the dungeon can throw at you.
D&D's got a lot of the former, though it grew up in the latter, and this is one of the friction points.