Counterexample: Kurt Heegener. OK, not a genius, but nevertheless a mathematician whose proof of a deep result (class number 1 problem [1]) was not accepted by his peers
Quote from [2]:
"In 1952, he published the Stark–Heegner theorem which he claimed was the solution to a classic number theory problem proposed by the great mathematician Gauss, the class number 1 problem. Heegner's work was not accepted for years, mainly due to his quoting of a portion of Heinrich Martin Weber's work that was known to be incorrect (though he never used this result in the proof)."
[1] https://en.wikipedia.org/w/index.php?title=Class_number_prob...
[2] https://en.wikipedia.org/w/index.php?title=Kurt_Heegner&oldi...