No. ARMOR, for example, also ignores it, so it's not part of one unitclass (it's simply bIgnoreBuildingDefense). Besides, if you do ever want to add a new unitclass, you'd also have to carefully change all the instances where this unitclass is used; combat modifiers, promotions, events...
Yeah, I was halfway through all that tedious stuff. Then I ran into an error that my editor couldn't even pick up... So I had to replace the file with an old backup, and redo an hour of modding that actually had no errors.
Oh, the joys of modding... 😜