This nails it.
The floor may be a lot lower now than it was during Vanilla/TBC, but the ceiling is still pretty high, and arguably higher, than what it was before.
I'm willing to bet that if you took the top current raiding guilds, and threw them into a vanilla environment without any of the current resources (websites/mods/etc) they'd still be able to beat the max content fairly quickly as the only real barriers would be time (how long it takes to gear up) and logistics (getting 25-40 people on consistently). But if you took the top raiders from the early days and threw them into Legion, they would struggle with the learning curve needed to stay at the top of the current raiding scene.
So the floor may be a lot lower, but the ceilings are now like up there like a cathedral compared to the two-story bungalow we had at the start.