There's no projection with Sixto, he's already got a ML elite FB, he just needs to get stronger (Stamina) and polish his secondary pitches.
Some guys are what they are, even out of HS, and it's just a matter of refinement.
Others are projections, and that's always risky, because sometimes the velocity never develops.
Prospects aren't cookie cutter, there's quite a range in timing of physical maturity and innate skills.
You can be big and strong, but never develop the arm speed to generate elite velocity.
Sales is a scrawny guy, but he has natural strength.