These buck converters seem to run hot and be a weak link. Couldn’t they be replaced with something more robust and potentially external? Or is it more complicated than that?

Agree, the Buck converters heat up quite a bit. There are a few ideas being discussed in the OSMU discord. Do check them out: https://discord.com/channels/1091348375301013615/1094385604982210633/1324379264765661264

Actually these are TPS546