Except Tom would need major time in recovery & refresher training before he could even really hold a post, let alone one that integral. Plus, it's not a competition between them. Tom isn't going to just settle being the ship's driver, like Wes was. Whatever job he got on the Gandhi was probably back on the command track he had been on
Please - O'Brien underwent 30 years in mental prison and nearly killed himself, only to be let back on duty within days following a chat with Bashir.
The Federation treats mental trauma like a hangnail.