No no, the performance is very important. A piece that sounds dull and uninteresting from one performer can sound full of life from another performer. Of course it helps if you have better source material, but that can only carry someone so far.
As for forgotten interpreters, before the days of recording I'd agree with you, but now we have recordings of greats from the past that's no longer the case. For example, in the case of classical guitar, people still admire the playing of players that are no longer with us, such as Segovia, and will still play their recordings. Whilst it's good to support new players too, a great performance is a great performance, it doesn't matter how long ago it was performed if it's still possible to listen to it.