Garcia's upside is probably higher than Stott, though his probability of reaching it is lower.
Garcia is a plus fielding SS who can stay there throughout his 20s, and that has a lot of value - top fielding SSs who put up .700 OPS are 3-4 WAR players, and given his batting eye, a .350-.400 OPB is not out of the question, so he just needs to add enough strength to approach .100 ISO power.
Williams is interesting, 3rd rd pick based on athleticism (i.e., high ceiling/low P of getting there), so there's probably some more upside left. Maton got rushed, should have started in AA and finished in AAA ball last year. Vierling is simply an unknown, great bat velocity but contact?
Question is how good of a read do we have on any prospect given the last two seasons and how it messed with player development, then through in the state of the Phillies development process.