That is laughable, nobody is making a choice between a $40k (usable) RED system and an R5, they are completely different markets. Now people that use RED's might buy a few R5's as well for crash cams etc, but nobody shooting RED's gives a damn about any non C Canon as a primary camera. It's as fallacious as saying they could be looking at a Samsung phone instead of a RED.
Canon make an entire range of C line cameras and lenses to cater for your "semi pro filmmakers" none of whom require 8k, the R line of cameras isn't it, the C500 II is the current darling at $15,000 but used C100's can be had for peanuts but the C line has specs and prices at every point in between to satisfy anybody.
really? Go look at how many semi pro and pro filmmakers gobbled up the 5D series DSLRs. A TON. A Red Monstro is $54k, only 35 megapixels and it’s sensor is alightly larger than the one in the R5. You don’t think filmmakers will jump all over a $5k camera that shoots 8k and 4K 120p with a 36x24 sensor and fantastic RF lenses? Please. I’m willing to bet more filmmakers buy the R5 than actual photographers, at least the first 6 months after launch. All the best goodies in the R5 are on the video side and Canon is clearly marketing it to videographers.