The biggest and most significant difference, to me, between VC4 and VC5, is that VC4 (with the exception of Solina) works well with Apple MainStage. It is stable and can be left running for weeks without restarting, and VC5 is unstable, has serious latency issues and eventually crashes, sometimes at very unfortunate times. In short, under MainStage 3 all the way up to 3.2.4, My experience is that VC5 is unusable and not worth $199. In my opinion, it is certainly not a suitable substitute for VC4.
In my case VC4 works, VC5 Doesn't.
I also don't like the new "flatter" UI and the fact that although you can magnify or reduce your screen, you cannot adjust the ratio to allow the entire Moog Modular V to be seen without scrolling, as it can with VC4. I would hope that a future update, once the stability and crashing issues are fixed, would allow the entire Moog Modular console (with or without the keyboard) to be seen in a more vertically oriented window.