<p>I dont think that claim really needs any evidence. It seems like common sense to me. If the LOR is supposed to attest to my potential as a researcher/scholar I think the person writing the letter should have a a significant amount of experience in research. A grad student will only have been doing research for a few years at most and probably has yet to prove themselves as a competent researcher. So I dont think they are in a position to accurately judge anyone else’s potential and therefore are a bad source for a LOR</p>