It depends on Gem genetics (gemetics). It also depends on whether individual gems have their own unique 'GNA' compared to other members of their type- whether Amy is any different from the Famethyst and whether they're different from the Jaspers, Carnelian, Agate, or other Quartzes we've met so far. It's difficult to say since a lot of gemetics points to types being essentially clones but ideologically that goes against the premise of the show, i.e. a lowly Ruby is simply inherently worse than a Quartz.
The Omnitrix could theoretically have multiple different entries for each type/caste, or there could be multiple forms akin to Perk/Murk Gourmands, or maybe there's only one entry from a high ranking (but not diamond) gem as the Omnitrix's original purpose is to facilitate communication and understanding between alien species, so something like an Emerald might help with that, as opposed to a common Ruby.
A proposed Cybertronian form might hit a similar snag (as they can vary in size from smaller than humans to massive giants) but the general consensus + the original purpose of the Omnitrix would lend itself towards "powerful enough to be respected and listened to, but weak enough to not be worshiped or obeyed without question" kind of dealio.