The imp familiar for Pact of the Chain is already quite powerful. In tabletop they can't even attack without your PC giving up their own action so they're already much better in BG3 right now.
Though I think they are bugged in that fly states it's an action but it currently isn't in game so you can actually get your imp familiar to jump after archers and kill/threaten them pretty easily right now.
A familiar that can go invisible at will and scout anywhere and which you can position anywhere you want before a fight is great already it doesn't need to scale.
Adding in other features they should have like casting spells from their location would be the way to go if you really want it to be better.
They aren't meant to be THE defining thing about your Warlock, and if they get too good your Warlock will feel like it has the power of 1.5 player characters and outshine other PCs too much.