One then does begin to question why we saw Wesley Crusher at the Conn so often. Even a field promotion to that position very likely wouldn't make him a the lead / chief Conn officer. The only in universe explanation I can think of is its possible that a galaxy class ship has so much support staff for that position that a lead isn't a required position on that class of starship.
It is actually very seldom in Trek that a more experienced officer replaces the one currently crewing a console, even in a crisis situation. Supposedly, Chekov never was the senior navigator, but if he happened to be sitting in the chair when things began happening, he would not desert his station.
Thus, perhaps we meet Wesley so often simply because Picard wants to give him flying hours, and the camera typically joins the heroes when it's Picard's own watch and he's pandering to the boy. Or when it's Riker's watch and he's doing his duty as the assigned father figure.
Interestingly, Wesley did desert his station in "Where Silence Has Lease" when things got more exciting - a sage decision because soon thereafter, the commissioned officer who replaced him was killed...
I think we're beating around the bush and really looking for an absolute fact where strongly implied facts are all we REALLY have to go on.
Naah. We're debating our definitions of "strongly implied".
All the heroes show at least passing competence on all fields. Doesn't mean any of them would have been a Chief Engineer or Chief Medic or Chief Astrobiologist earlier in his or her career. To the contrary, Star Trek paints these professions as "freakish", establishing that a good Chief Engineer is pathologically interested in his or her profession and for this reason really amounts to comical relief.
Riker and Picard both display competence with engineering minutiae, but of course it's Picard's job to steer clear of micromanaging, and Riker's job to do the micromanaging for Picard. Both also engage in esoteric projects that paint them as quite the renaissance men: Picard specifically immerses himself in various engineering challenges ranging from cargo management streamlining to deciphering celestial mechanics to the raising of new continents.
Its kind of like having an understand of computers from the Pentium Era and then being asked to work on a computer from the Pentium i7 era.
Which would mean that Picard and Riker would have equal odds of having been CEO in the past. It would simply naturally follow that Picard's knowledge would be more outdated than Riker's.
But really, there is only so much that one can include in a character's past before it all becomes ridiculous. Riker seemed like a driven individual before he found his niche on the E-D (and got Picard to replace the father-he-never-really-had); it doesn't appear at all likely that he would have digressed into engineering when he wanted to command, and OTOH it doesn't appear that Starfleet wants its skippers to have an engineering background. Could you imagine Kirk as a Chief Engineer?