They might say they wasted Momoya's time, but in the end it's an ensemble, so they succeed together or fail together. Psychologically it might be a burden for Momoya, but practically and realistically it's of little significance if Momoya himself excelled if most of them didn't, during the contest. It's not like he would have any special love for koto anyway, like Houzuki, for example. It's entirely possible Momoya will stop playing koto after high school.