I don’t think the counselors know much of anything if they are saying that. The top colleges are filled with Asian kids who played Piano or violin, want to be engineers or premeds and so on. That is not stopping them from getting in.
The problem I see is more of distinguishing yourself from other Asians. They need to also be involved in some group activities where violinists are usually part of Orchestras but pianists not always are. They need to join or start more clubs providing social service rather than stay with Robotics and Chess. Meals on wheels is a better club than HOSA for top colleges (this is coming from a parent whose kid started the school HOSA chapter).