They really look at tools and Davis and Marquez both have the ability to become special. Amaya is a solid player but his arm is avg and his hit tool lacks some contact. Nico IMO is over rated. His D is avg and lacks power. But has a plus hit tool and has shown the ability to get on base.Ehh, sometimes these rankings are superficial. Amya had a bad first half with the bat but last two months. The stick was doing well.
Off all of them it is really close between Davis and Marquez. Davis just needs to work on his skills. Mostly in Baserunning technique and his routes and reads as a CF. He has been getting by with raw talent. But IMO Theo should get him working with a guru in the off season to sharpen his skillset.
Marquez really lacks a strong 3rd pitch. His change is basically a fastball in the lower 90's. That is honestly the only issue with him. But he hits 100 MPH with a power curve.
So IMO these ranking are more so based off of current vs potential. Nico doesn't have the ceiling that those two have.