Looking at the compatibility list, two of the 3 games listed as broken seem to able to boot with underclocking, 3 of the 5 games listed as Intro/Menu seem to be playable with underclocking, and there are probably a few others in the other categories. Why are these games not considered playable, since having other settings be mandatory doesn't seem to exclude a game from playability?
To follow precedent on our compatibility ratings, we wouldn't want users to need to rely on under and overclocking for booting as that is an advanced operation. It's a workaround that users must manually do themselves, so by existing criteria it is not included in the ratings. That could change if it was enabled by default for those games, but as clock adjustment is changing the hardware we are emulating with all manner of side effects, I would definitely be against that and most other devs probably would be too.