I can definitely see your point, however i currently have beats solos that i got as a gift one year, and i find them very uncomfortable after a while. So, at least with full size headphones you get a better sound quality/better isolation. Since theres a trade-off either way, although, not all headphones are the same, so some won't be as uncomfortable and some won't get as hot, but still, since i can't try any headphone on for hours, i have to make the assumption theirs a trade off either way, and i'd rather it get too hot then just be painful to wear. Worst case scenario, i take them off and put ice on my ears for a couple minutes, and they'll be nice and cold again.
Also, is there a way to compare headphones via just a spec sheet (i'm used to camera/computer/phones/not highly opinion based stuff), which is pretty much why headphones are the only thing i've ever actually had to ask for advice on.
Another option is an IEM(in the ear isolating earphone) that isolates well. This would be my choice for use on a plane, train, or bus. I wouldn't use it walking around though, as I would want to use an earphone without isolation in order to hear my surroundings for safety reasons. The sports earphones with earhooks are my favorite choice for walking around. The earphones that don't isolate and don't have ear hooks fall out much too easily when one is active.