Do a test, take your R5 use a lens without IS and IBIS turned on for few days and let's see if you gonna have the same opinion. Especially if you are shoting mostly handheld in the move.
Afoy you do it you will notice how much ibis and is helps even up to1/400 of a sec. Depending on the lens.
I regularly use the original R as a second camera and the photos it takes are sharp as sharp can be. I shot a nonstop 3-day music festival on the R5 and lent the R to my second shooter, who was shooting with a pro camera for the first time. Comparing the files from the R5 with IBIS to the R's with no IBIS, there is no difference in terms of sharpness (resolution is obviously a different story). And I guarantee that any photo that would have been shot below 1/400th would have been blurry because of motion in front of the lens - not behind it.
IBIS is not a useless feature, but it's absolutely trivial for me personally. In the 73,000 photos I took last year, it only made a lick of difference on the two shoots I previously mentioned.
This is a bit of a sidebar however. The point to take away is that a hybrid is, by definition, neither fully one thing or the other. If you put orange juice and apple juice in a cup you're not getting 100% of either. You're getting a ratio between the two. There will be compromises, and if it wasn't IBIS it would have been something else. Look at any hybrid anything on the market and you'll find this to be true.
I think the bottom line is that if you don't want a compromise camera, you don't want a hybrid camera. There's plenty lacking on the cinema side too, if I want to hold it to pure cinema camera standards. But I don't, because there is zero expectation for this camera to be a fully fledged cinema camera.
What the R5C is is a remarkable hybrid. It appears that many people here don't want a hybrid despite saying they do.