It takes more than one person (unless we're talking about something that's just that bad. . .) to "overrate" something. I don't think the word choice is appropriate. What one enjoys is his own, personal business, and you're free to enjoy Feinberg however much you want. One can overvalue a composer's work in a number of ways, due to ignorance on some level or another, but a sheer, acousmatic "enjoyment" is entirely personal. The most common ways to overvalue a composer are overestimating a composer's historical importance, a composer's ingenuity, or the quality of a composer's music. I don't believe we're speaking about the first two, so we get into a mucky situation about gauging "quality" of music. Of course, some pieces of music we can simply state, as fact, as being better than others, but as is the case in that other thread regarding gauging difficulty of piano pieces, when the discrepancies in quality are smaller, it's nearly impossible for a person to be able to say definitively if one piece is better than the other, and when anyone does so, the rigors of their thought process should be immediately called into question.
Personally, I do think some of Feinberg's Sonatas are as equally deserving of performance as Scriabin's and Medtner's, Nos. 4-7 and 11 being the ones that seem to have the most depth and character. But it's a simple fact that the way the industry works isn't intuitive to a purposeful selection of Feinberg's (or Roslavet's, Protopopov's, Mosolov's etc.) Sonatas over Scriabin's. Pianists are brought up in conservatories where they learn standard repertoire, then go to competitions where they are expected to play standard repertoire. Also, the current issue of the relative obscurity of Feinberg means that a lot of pianists won't even be aware that there's a choice in the matter. All we can do is wait and hope that enough people fall in love with his music (as was the case with Scriabin himself, whose music became almost entirely obscure for several decades, or in the vein of what is now happening with Alkan).
Just an addendum: please bare in mind that this is, of course, Russian music, and not the sort of "Russian music" that the USSR would exactly flaunt. This is more the type of music that had composers being exiled to Siberia, or, more commonly, music that was burned. No matter how hard we might try, we are at least somewhat at the whim of what people (in this case, the former USSR) tell us is acceptable, or make aware to us.