Certainly, but you can still have some higher and lower bounds.
If you eliminate the danger of your portion (divided by party size) of challenges (monsters, traps, whatever) by whatever means, it's fair to say that you were useful. If you spend an entire encounter failing to eliminate the the danger of challenges at all (whiffing every round and drawing no fire, etc), it's fair to say that you were not useful.
That happens to everyone regardless of class or system.
I've seen people miss four or five times in a row. Crap happens.