I agree that Combs would almost certainly not have been very believable as an action hero; to that I say "Yay!" I am truly tired of Riker-type heroes, and so I think it would have been great if TPTB had come up with another idea for a first officer - Combs, a woman, a non-macho alien, SOMEthing besides somebody who's main job (most of the time) is to stick out his jaw in a manly way and say, "Shields up!"
Well, at least they eventually got the idea to make it a woman - since the subsequent 3 Trek shows all had a woman as either captain or second-in-command - it just took them some time!
Obviously, TPTB thought that there just a show HAD to have a conventionally handsome, male, human, white, extroverted macho action hero, and that captain was too intellectual and reserved... not to mention (shock! horror!) bald. Just shows that TPTB tend to be narrow-minded and don't really have an idea what the audience might like.
Eventually Riker the character had to morph into something else, not only because of his weight gain and the lack of need for him as 'the second lead' (by that time, if there was one, it was Data), but also because he couldn't really fit the alpha male concept, since the writers made him look unambitious, always content to be the first officer - which was, of course, the consequence of them trying to justify Riker staying on the show! Maybe it's because of the fact that they had nothing better to do with Riker that the writers starting giving him storylines like "Second Chances", "Frame of Mind" etc. But, while Frakes' waistline was expanding through the years, his acting ability was also getting better, so he was able to pull it off in the last couple of seasons.
As to Riker not being a leading man and TNG being an ensemble piece, the opening credits say that it stars Patrick Stewart and Jonathan Frakes, and co stars everyone else. It's interesting how Frakes kept that billing even when his character was overlooked and others (Data/Spiner) were massively more popular.
The same thing happened on
The Sopranos. Despite the fact that Edie Falco was clearly the show's second lead and, following the tragically completion of Melfi's arc in the third season episode "Employee of the Month," Lorraine Bracco, an increasingly unimportant supporting player, kept her second billing to the end, even though she's not in the final episode at all.
Bracco's role really did get smaller, but Melfi one of her greatest moment in season 5 premiere "The Two Tonys"... but there really wasn't much to explore about her relationship with Tony anymore, and she sank in the background, even though the therapy sessions were still an integral part of the show. The actual end of her storyarc is in season 6, though, when she changes her mind about treating Tony, but that felt a bit abrupt and just designed to give some sort of closure before the end of the show.