It's also possible that the original Riker's career skyrocketed mostly because Admiral Pressman was bribing him with promotions to ensure his silence. And either he wouldn't go to the same trouble with Tom Riker because the same perks wouldn't have the same effect on a man whose life and career already were completely different - or because he simply didn't have time to do anything about Tom before "The Pegasus" happened.
My take has always been that Riker's meteoric rise in rank was
a series of lucky coincidences, as well as Riker being somebody who puts himself 'out there'. The Pegasus
incident seen him, as literally a fresh graduate from the academy, take a critical role in protecting his captain when the majority of the ship's crew mutinied. Whatever the moral implications of the incident, and I don't doubt Riker stewed over them for decades afterwards, once they got back to Earth his standing up for Pressman and his keeping Pegasus
a secret, he probably found a good word going in for him, hence his first promotion. Then the Nervala IV incident happens and he gets another commendation, resulting in his making Lt. Commander. If you look at the timeline, including the events of "Best of Both Worlds" where he does make Captain, then Riker goes from Ensign to Captain in the space of about nine years. He was probably seen as Starfleet's golden boy. I don't doubt that his decision to stay aboard Enterprise
as her XO was seen as something of a surprise by the brass back at Starfleet command.