Leaning on the neck really isn't a big deal. The string tension puts about a hundred pounds of tension on the neck. The weight of the guitar leaning in a nearly upright position is negligible.
I keep seeing this repeated on the net but I don’t see the threat. Any outside wall in a home here will be constructed in such a way that there won’t be a surface temperature or area humidity issue unless there is a heat source in the immediate vicinity, in which case it’s a matter of heat source not outside wall. It’s also not common that an instrument hung in hanger would even be in contact with the wall, but rather they hang an inch or two away from the wall. If the atmosphere in a room varies so much that it’s unsafe for instruments, there are bigger problems than the safety of instruments.If you hang to a wall, avoid outside walls.