On power potential:
Campbell
A+ 558 SLG
AA 582 SLG
AAA 468 SLG
20 HR in 2024
Mayer
A+ 524 SLG
AA 480 SLG
AAA 452
8 HR in 2024, max was 13 in '22 and '23
No matter what offensive stat you want to look at, Campbell was better offensively in MiLB than Mayer.
Not sure what stats you want to go on for Mayer defensively.
Here's his scouting report from SoxProspects: Instinctual defender with fluid actions. Looks like he is gliding on the field. Soft hands and solid footwork. Moves well and has plenty of range for shortstop. Confident defender; will take a flashy infield. Some long-term concerns about his ability to stick at shortstop as he matures. Organization appeared poised to get him some reps at third base midway through 2024, but injuries, including the one that eventually ended his season after July 30, effectively scuttled those plans. Potential above-average defender at short for the foreseeable future.
His 981 Fldg Pct '25 at SS (Story is 973 right now) would be top 10 in MLB this year, but you'd rather slide him over to 1b. 🙃