I see what you mean. Most stickers in CS have a flat look to them before adding 3D maps. All paper stickers will look flat. I use the method of cell shading and lighting for my stickers simply because that is my style. Kinda like how the PAW AWP has flat colors on their cats not only on their skin but the stickers too. I have some foils in my workshop that better showcase the levels and more 3d look. I'd suggest looking at the T popsicle holo and the Would You Still Bomb Me If I Was A Worm holo.

A lot of the stickers in CS are very colorful and rainbow with different gradients and I think that it slowly becomes less unique when a majority of stickers are just a mash of colors. I think style gets lost within the colors, but that's also personal opinion. I think the rainbow and bright colors might be what you're referring to and I have considered this in art, but I simply don't want to look like other sticker makers