I mean, if you start including insects the tree on land is way deeper. There's more size niches in land photosynthesizers for whatever reason, so there's more variety in herbivore size too.
Not true at the extremes I say because pelagic ecosystems have small single cells handling their primary productivity, you have microscopic copepods starting the grazing at the same size as the smallest herbivorous insects, and until recently you had stellars sea cow weighing in at 8-10 t, more than an African elephant.