Okay, I get that, I think the VAR is a matter of cost isn't it? The cost of providing VAR facilities at every club in the earlier rounds and the replays to ease potential fixture congestion... I'm not saying it's right, I don't think it is but there is an explainable logic around it, same for group to knock out.
I can't fathom why tac-subs are okay in the group stage but not in the knock-out stage though, can you help me out?