I think Tom works on Voyager. I'd be willing to bet he'd clash with Riker considering how we saw how he reacted with Levelle.
I think that had Riker been on Voyager, he and Paris would probably have gotten along royally.
Ensign Lavelle was just that: an Ensign. He had accomplished nothing in his short career. Meanwhile, Paris is an accomplished pilot, one who clearly has earned the ego that he carries on his shoulder. That's exactly the kind of guy Riker would like.
As far as people stepping into roles in critical situations, I think that was overall one of the failings of Voyager. There should have been at least three pilots on board, one for each shift. We never really meet any of them (except Ensign Jenkins), but one wonders what they were up to whenever a pilot was needed. Kim should never have been Ops department head as a freshly minted Ensign, which isn't even as a result of the Caretaker because he was declared the Ops Officer right out of DS9. Especially considering there were other Ensigns who would relieve him from time to time.
So, Voyager dropped the ball.