I'm a fan of Hindemith's music. At least some of it. But it doesn't rank high on my list of greatest music or music that I listen to quite often with great pleasure. Yet it is said Hindemith could play anything he wrote on any instrument he wrote for. He was a virtuoso violist, by the way. Yet I find his Der Schwanendreher (a concerto for viola and orchestra) one of the least interesting pieces, and I can't recall the last time I listened to it. Decades ago, I'm sure. (I am reminded by this very remark that I am due to re-hear the work -- which might possibly change my opinion, too!)
In contrast, I find Berlioz's instrumentation fascinating (though I am not a big fan of his music overall), and that of Rimsky-Korsakov fascinating, too. Yet I wonder how much of what they wrote they could play themselves? Not much, I suspect.
Of course, pianists like Chopin and Rachmaninov seem to be able to write well for their instruments. And though Chopin may be less skilled at orchestrating, Rachmaninov certainly was not.
I greatly admire several orchestral works by William Walton, especially the First Symphony. And I feel that his Viola Concerto blows away anything Hindemith wrote for the instrument. So, who can say?
Some composers write well for certain instruments or combinations of instruments. Some produce great musical ideas that rise above any single instrument (I'm thinking of Bach's music for undesignated resources). Some music interests me and some doesn't. I prefer to let the music speak rather than worry about the instrumental skills of the composer.
Then there is the issue of Rodrigo's guitar concerto, the Aranjuez. I don't know if Rodrigo played guitar, but I do know he was blind. Yet I can't think of a more visually alive piece of music than the Aranjuez. I can never listen to it without "seeing" images of Rodrigo's homeland.
Such is the wonder of music.