I just got the RF version for my R5 after six years of beating up the EF IS II version. So far the image stabilization is worlds better, and it does feel like the RF version is more responsive to autofocus. Image quality-wise, I think Canon's sole focus was to reduce weight/size without impacting image quality. The EF II and III were always great lenses already.
I know you already said about the weight, but for me the absolute biggest reason I took the plunge on the RF was its form factor and balance with the R5. I'm just blown away at how much more comfortable the 70-200 is to use. Plenty of scenarios where I would have left a 70-200 at home that I now would definitely bring it with me. I personally hate the handling of an EF 70-200 on an adapter on the RF. It's a long enough lens already, adding the adapter just makes it look longer and more unwieldy. Not a problem to me with the 100-400 or a supertelephoto, since those lenses come out when reach is really a question, but a 70-200 is such an everyday daily-use lens that it really is a great experience using a lens that feels more like a 24-70.