I agree. If I had any intention of getting seriously into video, as a Canon user, I'd probably go for the R5C. But I'm purely a stills photographer, so I'm very happy with my R5, which is I think the best camera in Canon's stable for my wildlife, landscape and macro photography.If video is your primary use case, the R5C is a no brainer even without IBIS. If you plan to shoot a lot of handheld photography at lower shutter speeds (low light) more so than video, stick with the R5.
But none of this gets away from the fact that there are many users (e.g. wedding, event and advertising photographers/videographers) for whom it's highly desirable for a camera to be equally competent at video and stills.
And the questions still remains - if Nikon Z9 and Sony A1 can shoot continuous 8K without needing a fan, why couldn't Canon? Arguably, the Nikon doesn't need a fan simply because the larger body dissipates heat more efficiently, but the Sony is even smaller than the R5C, yet manages without a fan.
And if Sony and Nikon can do hi-end pro video work without compromising stabilisation for stills photographers, why can't Canon?
I think the truth is that Canon could easily have kept IBIS in the R5C, but chose to omit it for product segmentation and cost-reduction purposes. As a result they have produced a great hybrid camera at a price that undercuts their main competitor Sony. But in my eyes the Nikon Z9 looks a better tool, whether for stills, video or hybrid users - and it costs about the same as the R5C.