There are several hundred different types of snaffle, and it is more down to horse's mouth conformation, preference and rider as to how 'strong' a bit is anyway. I have in my possession a twisted wire W snaffle - no way could you call that mild and no way I would ever put it in a horse's mouth!
Sorry, not much help but IMO it is far too simplistic to look at bits on a spectrum of mild to severe What problems are you having?