Giolito is a textbook example of why velocity doesn't matter. Between 19-21 he was able to throw change ups over the plate, avoid hard contact and get a decent amount of swing and misses by getting ahead, getting people to miss pitches over the plate (usually with a change) or get them chase fastballs out of the zone. For the last two year's he wasn't able to get the same results on the change up and his fastball started to get lit up.
Similarly Cease was able to work off an elite slider in 22. If you have an elite pitch you can throw over the plate, get strikes and not get hammer you'll do just fine with any fastball as long as you have at least average command.