Ok, maybe I'm just to spoiled by my previous experience then. I never had any problems getting patches upstreamed relatively quickly, but then e.g. meson or picolibc are much smaller than LLVM and patches are simpler to reason about (I know some compiler construction).
Remember that in my comment above, it’s assuming a speedy review. Release schedules are still a thing; I’m not at my computer anymore, but IIRC, llvm releases once or twice a year, so that’s the inherent limit of making it into a release, not necessarily the review time.
Thanks for the answer.