Tobias wasn't aimed at anime fan teenage boys, that's a huge distinction between the two situations. Angry 15 year old boys who wanna see explosions do _not_ want their power fantasy ruined by someone pointing out how fucked it is.
nor do angry 40 year olds who should know better but I am being charitable and assuming most of the rage was from actual teenagers.
Tobias was written for kids aged 10 to 15, who are choosing to read for fun, not because they're being forced to, in a series marketed as being fundamentally about the child soldier stuff, kids fighting aliens and getting worn down by violence was part of the pitch. Animorphs was Red Dawn for kids, making a point about warfare and stress and being a cool alien conspiracy series.
It wasn't aimed at a demographic primed for the same sort of toxic masculinity, it wasn't aimed at people who would refuse to think on sheer principle because they want their cartoons shut up stop preaching, it wasn't aimed at people who had gotten a million similar meals before and expected the recipe to be followed to the letter.
Make an R-rated 90s Animorphs anime series in the same target zone and audience, and you'd have those same people hating Marco for being such a coward, why's he bitching, turn into the gorilla and rip more arms off, dammit, that's why we're here!