::blink::
If there's one "discourse" that, in my experience, has dominated D&D, and certainly 5e, it's "martial-caster balance." Players want equally good options. Players don't want "traps" that make their characters less capable than those that chose other options. Players want niche protection: If they play a rogue, they want to be the go-to guy or girl for sneaking and such. If they're a greatsword fighter, they don't want CoDzilla showing up and dishing out more damage, but also tanking damage, healing, flying, teleporting, and doing just about anything else that comes up better than they can.
I'm not saying every player cares about these things, but I'd confidently say most do, in my experience, and I think the designers over the decades have recognized it and attempted to address it, with varying levels of success. At various times during the game's history, it's been possible to mix and match some things without running afoul of normie D&D player balance concerns, definitely. That doesn't mean most people are going to have one Lore Bard with 6th-level Magical Secrets at the table alongside another that has to wait until 11th level and not run into a problem. Put it this way: I'll bet you good money they don't try to run AL that way, and I certainly wouldn't run my table that way.