I have a spot in my bag for my adapter. In most cases it's left on the camera, particularly since I primarily use just EF with my C70, though, since I also have the full frame adapter, that's just more added complication (for better and for worse).
With the R5 I'm talking mostly still photography shoots in studios with different sets and rooms, and needing to go from set to set without a dedicated assistant, changing lenses quite often, and having to keep track of where the lens mounts are. When I'm switching from the EF 50mm to the RF 28-70, I'm not going to pause a photo shoot so I can take the mount off the lens, run back to the camera bag that's 40 feet away from me, store it in the pouch in the camera bag, run back to to the shoot, take more photos, then when it comes time to put on the 70-200, run 40 feet back to the camera bag, put that mount on the 70-200...Rather, I'm going to have a small lens bag nearby where I'm shooting, or just place the lenses I'm not using on a nearby piece of furniture, then when I need to change from the EF 50 to the RF 28-70, I'll put the EF 50 on a table, next to the 70-200, leave the EF to RF mount on the 50, then, well, maybe I want the 50 again five minutes later, hey, it's already got the adapter on it, no wasted time changing adapters, but then later, I want the 70-200, well, now I need to change adapters, where did I put the 50, oh, there it is, over on the desk, took a bit of time to find it, probably less time than running back to a large camera bag in another room, but, now I've got to switch the adapters, well, this is taking time. If I just had one lens mount to deal with, then, I wouldn't be wasting as much time.
If we had to choose between having gear that had 30 vital pieces of equipment needed to accomplish the job, or 5 vital pieces of equipment, all else being equal, 5 would be preferable. The more pieces of equipment you have that will make or break the job, the statistically more likely you are to forget to pack, lose, have broken, stolen, etc., a vital piece of equipment. Sure, you can take precautions, write check lists, do whatever, but all I'm saying is that the less vital pieces of gear, the statistically lower chance you'll have issues if a piece of gear is not present or not working properly.
Because the R5 is better for stills than any Canon EF bodies, and I want to use the RF 28-70, and I prefer RF mount, as I said. I'm just saying it can complicate things, depending on one's setup, such as mine, which involves using both EF and RF lenses on an RF body. I'll take the tradeoffs and complications, but I'm also not one who goes around singing high praises for the RF mount, especially for video since I'm mostly using EF lenses along with cinema lenses in EF or PL for video. Maybe I'll change my tune if or when I get the RF 24-105 2.8, but aside from that lens I don't see big advantages with the current RF lens lineup for video.