Well first off the features do work. One of my hobby-focused environments is high-speed dog sports. I can guarantee you once I somehow get my hands on an R5 that I'll be playing around with 8K, 4K120, and 4KHQ video though mostly I will be taking stills. Video length (dogs move fast for an exercise then it is over) is always less than 1 minute. I'm confident I'll be able to take these videos without overheating issues. And worse case if It does I drop down to 4K30. There are other definitions for the term "work" other than "I filmed a full length movie in the sahara desert".I generally agree. But, I have a problem with any company that offers any feature that isn't ready for prime time. I think it was more than a bad marketing decision. I think it was a bad engineering and design decision. No matter how many disclaimers you offer, it's no substitute for having a product that works. If they couldn't make these ridiculously high resolution and frame rate modes work, they should have just left them off.
My perspective is different that the majority on this forum, but I see this as a case where they let the engineers and designers drive the marketing. "Ooh lookey what we can design! Never mind that it's non-functional in the real world, people should just adapt." No. You should engineer the product to work or not include the feature.
But consider if Canon did what you suggested. They didn't offer any video mode other than 4k30. How many MP would the camera have? The 45MP number was clearly chosen because it matches what is needed for 8K video. With that constraint gone Canon might have gone with the 50+ MP--something matching the 5Ds for resolution. In either case the 4K30 would involve line skipping and the YouTube videos would all be about how Canon's video quality sucks compared to Sony's. So would they drop the MP down to 12 and essentially make a video camera?
People always argue that stills cameras get video features "for free" but that really isn't the case. Once you decide on a high MP sensor for stills then video is either compromised by line skipping or it is cutting edge (8K / 4KHQ) and there are heat issues. Canon had to choose between a 45MP stills marvel that either did "crappy" (compared to the competition) video or both unlimited "crappy" video and heat limited best-in-class video. I don't think it is hard to understand why they went with the latter.