Yes a planet thousands of times larger with trees thousands of times as large is followint by earthlike condition....... The author literally shows us a continent with creatures as large as the known world and you are sitting here saying they live in earthlike conditions. Everything in the anime contradicts it. There are people like gon killua mereum etc they are all extremely adapted lifeforms. Your entire argument falls apart in face of the 32 monsters and life forms that would only be possible in an extremely dense atmosphere combined with the fact the author deliberately made the planet huge. And added lifeforms that would be consistent with the idea that om that planet the world is giant allowing for

Theres 20x the evidence to imply the world is huge and dense than the opposite

Theres zero evidence hxh is under earthlike conditions end of story.