Holy **&t you are shooting Paris FW? Now I am seriously jealous, I shoot all of the big fashion shows here in FL with the biggest being Miami SW. I was invited to NYFW and Paris FW, but no one was willing to pay for my travel. For fashion shows I've got my kit down to a single Lowepro bag and a tripod....I shot Miami SW with the C70 and R5. This year I plan on trying just the C70 and R7. In the bag I've got my mini XLR shotgun mic, Sennheiser wireless transmitter/receiver + lav mic, side handle for the C70, C70 in a cage, and R5 is just rigged with a shoulder strap for photography. I was able to shoot all of Miami SW, interviews, vendors, models, promo videos, etc. with just that setup.
As far as color grading VLOG goes, I think anything can seem like anything if you pixel peep, if you just get out and shoot and grade until the footage looks good to you and your customer that's all that really matters. When looked at from that viewpoint, VLOG was no worse for me than CLOG.
This year I plan on trying the R7 to see if I can add a bit of walking as well without a gimbal and to be able to switch between the R7 and C70 for video. The R7 will take over for handheld video and photography, C70 for interviews and the runway walks. I tried the monopod thing and couldn't make it work, monopods feel so limiting and still not as stable as a tripod or as dynamic as handheld, even without IBIS I would rather handheld over a monopod.
It does sound like the R3 checks a lot of boxes for you as well, you definitely cannot go from a fully rigged R5C to photography very easily. I don't get why the R5C is so bad on battery life; it doesn't have to power IBIS and its the same sensor as the R5. You could set it up like I did with the C70, where it slides easily into a nato rail V-mount battery setup for long form and slides off into a handheld setup for shorter shoots and gimbal work. That is also how my R7 is setup.
Below is a picture of my setup. The S5 is in the picture but the C70 and R7 both slide right into the same top tripod mount. I use the bottom tripod plate to mount the whole thing to a tripod. For fashion shows I setup the tripod and nato/v-mount (and to hold my spot in the pit), then slide off the camera and go shoot b-roll until the show starts. Of course you still would have that IBIS problem with the R5C and the slower AF......so there's no way around that if you go with the R5C