I had the 6D Mk1 and now have the RP. I shoot mostly landscapes.
The RP is a great camera. It's smaller and much lighter than it's DSLR equivalent.
The RP is basically the 6D Mk2 in mirrorless form, so it's the same sensor and almost the same functions. But the EVF means you can zoom in while using it (to check focus for example), you can judge your exposure easily as it gives you pretty much what you'll capture in the EVF.
Last year I used the Canon Test Drive programme to borrow the RP and RF 24-105.
Here's the RP next to the 6D, both with their native 24-105L lenses.
View attachment 325537
If weight is a concern for you, then it will be of interest that the RP combo is 200g lighter.
The body is definitely smaller, but you don't save quite so much in size on the lens.
The size advantage starts to get negated once you add in an adaptor. Currently I'm using the EF 24-105L (Mk1) on the RP and with the Viltrox adapter (the Canon adapters are tricky to get at a decent price currently), that adds about 1.5cm to the length of the lens.
The EF lenses work very well with the RP on the adapter, and actually focus accuracy is better because it's focusing via the dual pixel AF on the sensor rather than a seperate AF sensor.
As for cost, the RP can be had for £800 or less s/h vs about £1000 for the 6D Mk2. The EOS R is about £1200 s/h.
RF lenses are a bit tricky to get hold of at the moment, depending what you're wanting. I'm still trying to get hold of the RF 24-105L for a reasonable price.
The 24-105L is a superb lens for landscapes, whether it's the EF or RF version.
As for portraits, the RF 50mm f1.8 is great and only about £200 new. The RF 85mm f2 is great too (another one I've tried on the Canon Test Drive programme), but that's about £550ish.
The EF 85mm f1.8 would cost you about £200 s/h.
I guess it also depends on what gear you have currently. Do you have any EF fit lenses? Do you have a crop sensor Canon?
If you go for an RF mount camera, can you afford to get all new lenses or do you have some EF glass you want to keep?
The 6D was a good camera, the 6D Mk2 is a better version, though arguably the main improvement is the AF system. However if you get the RP, you get the smaller body, higher MP/newer sensor and the much better AF system.
And you're buying into the new lens mount system, meaning it'll continue to be "current" for longer. EF will still be around for years as there are so many good cameras and lenses, but Canon has already discontinued a few EF lenses.