I think the idea "if a feature works on at least one of a creature's types, then it works on the creature as a whole" is perfectly fine and a good way to simplify rules problems, but if they want to go this route, they need to explicitly answer two other problems:
1. Some features specifically say they /don't/ work on certain creature types, as opposed to specifically working on certain creature types. Should "this doesn't work on undead or constructs" be interpreted as "this works on anything that is not an undead or construct"?