In many fighting games, the lackey character either provides no real plot significance, usually with a joke ending, or betrays the boss character, I've found. Futo and Ichirin are merely going along with what these types of characters usually have for a story in fighting games. If anything, the fact that their routes acknowledge how they were completely worthless might be a lampshade hanging on how worthless the lackey character usually is to the storyline of a fighting game. That said, in terms of storyline, I'd rather have a lackey character that doesn't contribute to the overall plot than a character who isn't connected to anyone at all and doesn't contribute to the main plot (which fighting games are absolutely filled with, these days). I don't think Nitori particularly falls under this category though since if anything, she at least has a purpose in symbolizing a character who really hates all this religious hallabaloo going on. Marisa probably does, though.
In terms of gameplay, however, it's natural for most fighting games to have characters who contribute nothing to the plot and aren't really connected to anything significant, if only to fill out the roster with more characters to play as as well as tradition. Again, Marisa.
After all, as the cast gets larger, you can't have everyone be plot relevant. Take a look at Scarlet Weather Rhapsody, where a vast majority of characters were just joke routes or had storylines taht really could have been removed and the overall story wouldn't have changed much.
