If you think about it, Krillin is inherently untrustworthy and unreliable. It is nice that he was able to overcome his bullies, but he that is about it. Later on, there was one crucial moment that he could've saved the world, but he didn't kill Android 18. If she turned out like in the other timeline or if Cell won, or anything went wrong, than the one moment he should've done something, he failed