But again, I must point out that Crystal DID "drop" the Piano half way through that last performance, and the second half of that performance was the better half by far.
We can call it a crutch that she's always had one around, be it harmonica, guitar, piano or some combination, sure, but we've at least with HER seen an indication in that minute or so she was standing away from the Piano that it was no problem with her (go rewatch it on YouTube--she gets up exactly half-way through, and looks fine in that second half). That's not necessarily true with Andrew and Casey, since I believe the one time we saw Andrew sans instrument (Miley week), it sucked, and... have we seen Casey without one yet? I don't recall. If we have, it wasn't very memorable.
IMO Crystal IS better than your random street corner musician. If you search out her own original music online, IMO I think it proves it.