Are well-intentioned fuckups by boots treated more leniently than fuckups by professionals?

As long as the recruit is trying hard and is otherwise capable .. in my experience, yes.

but there's always been a lingering sense of failure. We all have our crosses to bear, I suppose.

We all have them: what I've achieved in life (so far) would have been a lot easier if I'd gone to college instead of joining the service.