"I like C&C in RPGs, unless it's about actual choices with gameplay consequences
The spots for the Round Table should be free. It's not like you gain much from that alone, gameplay-wise. You still have to take knights with you on missions or put them in the Training Grounds, which also means committing limited resources there (to open more spots and to train them). But, hey, let's pretend like it's a good idea, because some idiots think it's some sort of C&C™ when you're pretty much forced to dump resources just to keep your knights relevant in the game.
"I need to have every single companion, every item, and be able to access every piece of content in a single playthrough otherwise I'll cry"
You consistently favour every single line of thought that led to the decline of modern RPGs. No wonder you're a Disco fanboy.
Devs limited knights you can have on purpose, this is also why the game has a morality chart that gives unique knights for different alignments, the systems work together to force you to make decisions and commit to a specific playstyle on a playthrough. This is a fundamental design decision which the whole game is built around.