So I read through this, and the whole time I hear my old bio teachers lectures in my head.
Evolution's trippy; Andalite physiology doesn't really mean that the planet must be dangerous, it just means that those traits encourage, or just happen to be on creatures that survive.
Had they could have evolved all that stuff anywhere; if they had happened to be from earth and evolved like that, I'm betting they'd be okay in general. If they happened to be from the land of buttercups and pixie dust, still they'd be okay.
Earth is plenty dangerous, but as any Andalite would tell you, the dominate race is physically laughable.
Decked out traits is a lucky convience. If it were about everyone evolving to danger, all the things the Andalites evolved to out match would evolve to keep out, and be more dangerous. And then the Andalites would evolve again. And then the other things. Then the Andalites....didn't turn out like that.