I suspect that applies specifically to their cloud rewrite which was apparently a bloat of JS libs and hundreds of requests even by Atlassian standards. The on-prem self-host Confluence I've used is still pretty snappy and pleasant to use and without throwing an absurd amount of resources at it. We do have quite a lot of actually-useful documentation in it.

That said, Atlassian is busy relentlessly raising the price for self-host to push people into their cloud roach motel, so we'll probably be on some alternative (either FOSS or commercial, but self-host) soon too.