Gatomon is a champion level Digimon, and adult level Digimon. Her character design is chibi in nature. I get the rookie level Digimon as those are child Digimon.

Speaking of small cute cats, what about palico? The cat chibi that helps out in monster hunter? How do you age up them? Do you even age up them?

Honestly the mods just need to get together and make some info graphics for different trouble species before they can go about moderating them fairly. Without a visual guide in place, the rules become subjective to prejudice and/or bias against artists and/or species.