Eh, being useful in combat isn't actually that hard, due to pure action economy.
Reflexive defend-other charmtech also help to avoid making weaker character in liabilities.
I instituted non-charm reflexive defend other in my games for this reason. Though I'd disagree on the additional actions always being helpful because of how costly protecting such a character can be. Depending on the enemy, it can easily rise above whatever benefits the character's actions provide.
The difference between a minimal/non investment character(excellency and nonartifact light weapon) and any enemy who can fight back is large enough that such characters were an active hindrance in most major fights. Even after reflexive defend other came into play, they became one as soon as their mortal bodyguards went down and the loss of mobility for the heavier combat characters mattered. Assuming, of course, it was a fight in which such things could happen given the personalities and factions involved.
One party of mine figured out a good solution to this, give the non combat character super heavy armor on top of body guards. Now they were no longer worth throwing attacks at because taking them out would require effort, and motes, better spent elsewhere.
The player was on board with this, but not also picking up a grand kill stick to force perfects based on luck with, because she felt that wanting to keep herself safe was in character and giant weapons were not.
Like, it sounds like Storyteller certainly isn't helping, but won't this sort of thing always be an issue where any attempt at gradiating player ability comes into play?
I've seen systems, mostly more narrative ones, where degree of success and failure were much less binary or at least had wider scales of odds.
My favorite are the new fantasy flight Warhammer Fantasy and Star Wars games. They need special dice to play, but different faces of the die providing different results made it so that failing an action often resulted in some sort of benefit on the character's next action because there are multiple different ways that positive and negative effects happen.
Other systems, GURPS comes to mind most easily, give many methods of manipulating the probability of a given result in exchange for specific benefits and penalties the action takes.