After watching TNG and VOY, there is a rather major discrepancy: in TNG, there seems to be no consistent helms officer on the Enterprise-D, apart from when Wesley is in charge. It seems to be some random Ensign that last about a week/month before a new one is put in charge. Yet, in VOY, it's always Tom Paris (as is the case in TOS and ENT). Why is this the case (possibly to give Ensigns experience or something)?
- Because the producer's gave Robert Duncan McNeill the role of Tom Paris, helm officer of the U.S.S Voyager and viewers don't want to see story-lines about random pilot of the week, nor did anyone want to pay someone else for a speaking role when you're giving McNeill the paycheck.
- It's often stated that Tom Paris is the best pilot they have onboard so that's probably why he ends up as permanent helm officer after the last one gets herself killed in the Pilot. But as we see, there's different shifts over the course of a day on Voyager and Paris must have counterparts driving the ship when he's taking a nap. We just don't see a lot of these other shifts because no one wants to see episodes which consist of the main cast sleeping.
- There's also a big discrepancy between job availability/advancement between U.S.S Voyager and U.S.S Enterprise. A lot of people are stuck doing the same jobs on Voyager that might have changed to different jobs on Enterprise, but probably not.
- Don't forget that on TNG we had regular helm officers too. In Season 1 we had Geordi flying the ship, while in Season 5 and 6 they had Ensign Ro. Wesley filled the role in Seasons 2-4. Also if you check out this link for Flight Controllers you can see that other helm officers had reoccurring appearances, so all were probably having off-screen adventures onboard the Enterprise between their appearances.