There are many sites that have compared card speeds etc for different cameras with Angelbird (a relative newcomer to the market and has only USD3m/yr revenue) achieving high scores. Given your feedback about Canon's active engagement to remove incompatibilities, ongoing lockup reports and Canon's reluctance to update their support page, I am hesitant to buy any card not on the list.
I see your logic, but I see it a bit differently. Angelbird has (and soon, reportedly, ProGrade) user-updatable firmware. To me, that's the big deal. There's a higher chance my Sony Tough card will get bricked with a new camera firmware release than an Angelbird card. Delkin had a policy where they would swap out your old card for a new firmware version, if the new firmware was relevant to your use. They (Delkin) have a 2-day service policy.
By contrast, Sony never paid up on a "lifetime guarantee," pricey SD card I purchased years ago that just didn't work. They make a really nice CFexpress card, but I'm not counting on any support for it.
The process of making my own CFexpress card out of parts was pretty educational. One big takeaway: it's really easy to buy the right size of SSD drive and just slap it in. What this means, though, is that you're relying on a controller designed by some other company and have no control over firmware. In my case it was Toshiba, and the SSD chip was harvested from someone upgrading a video game console.
Only those companies willing to go through the trouble of writing their own firmware layer, and purchasing smaller-lot, custom configured SSDs, additional flash memory, etc., and creating a mechanism to re-flash that firmware will have this capacity. Personally, I want to own those cards, because they're writing that firmware specifically to optimize the performance of my R5 and someone else's Z9 - not that game console.
I have high hopes for the new ProGrades for the same reason. I was told we should see them this summer. If you're looking for Canon-blessed brands, that might be the optimum choice for you.