Main problem i have with your examples GM4HIM ... Is that you are counting with party of 6 ... you dont seem to take it as option, when you adjust mob stats, but as the only option. :-/
I mean, yeah cool if they adjust imps and intellect devourers, party of 5 or 6 will deal with them just fine.
But what exactly will do that player, who dont want to have so huge party right from the start? Or who just wants to create single custom character?
No. I get you. I know there are people who want to just play the game with a party of four or by themselves. The problem is you can't build a game on that unless you're going to create some sort of level of difficulty options. You have to start with a baseline. And that's my point. The baseline should be a party of six with normal stats based on 5e. Then you can create an option for four players or a single player mode or whatever with stats that are nerfed.