The A7R III is not selling for $1600, it is selling for $2,998 and is a totally different level of camera than this new RP. Apparently you mean the A7 III, which of course does not quite have the specs that you state. And no Canon lens with adapter works flawlessly on a Sony. And exactly what this has to do with Canon's M system I have no idea.
Your post is nothing more than a meaningless/misinformed advertisement for Sony, in my opinion.
I'm not the one misinformed, you are the one misreading my post! Go ahead, read it again, this time with more care. I'll wait...
In fact, the Sony that most closely resembles the RP in specs, the A7II, was selling for only $900 during the holiday season (currently $1000) and also, just like the A7RII I mentioned in my previous post, it has IBIS, "some" weather sealing, and better DR than the 6DII. I didn't mention the A7II in my previous post because this camera only does Sony's flawed compressed RAW files, which to me is a worse offender than the 6DII's limited DR. If Sony updates the A7II's firmware so that it's able to do uncompressed RAW like they did with the A7RII, then this dirt cheap camera (it will most probably hit $800 very soon) will be a very hard bargain to beat.
What does all this have to do with the M system? I own M system hardware that I really love, but if one day I decide to "move up" to the R system, nothing that I currently own, apart from flashes and adapted EF/EF-S lenses, will work on the R bodies. Maybe Canon decides to make an RF to EF-M adapter so that I can use my iuuuge R lenses on my tiny M body, but that could also mean that I can pretty much kiss the possibility of ever owning an EF-M native 50mm lens goodbye forever. It's like the FD to EF transition repeating all over again. So for M system owners, Canon has failed (again) to keep us captive to the brand, providing us a clear, effortless upgrade path to the R system, instead we have to either sell everything M system, by which time we might as well as move to another brand like Nikon, for example, or keep it as a stand alone, which won't make any sense if Canon decides to do R bodies even smaller than the RP.