I haven't put much thought into the minor factions yet, but yeah they're mostly going to be filling niches that other races don't expand on, or to add to races that don't have a feature (like Wizzrobes mages to help out the magic-less Moblins).
Volvagians are definitely going to be a heavy unit group, focusing on fire damage and siege.
Subrosians will mostly focus on mining and upgrades, with a boomerang unit and some weak melee stuff
Huskus will be a strange mix of expensive units with a high damage output and swarm units that are almost useless.
I agree that 0ad is wasting its potential, but I don't think the scenario should be the absolute priority, I think the better immediate step is working out the multiplayer mostly an anticheat, account management etc to push the game to mainstream platforms like steam.
once more people notice, the additional interest should drive people into creating content and improving the game, the opposite is having a well polished game that no one knows about.
@Red Wolf, some clarification:
Regarding 10 (Wall towers could be upgraded to fire at enemies): I think this was so in the past (someone said "left-over from old wall towers being able to shoot" in another thread), so there were reasons to change it. I think there are issues on how Palisades, Walls, Towers and Fortresses work, so we might see some changes at some point.
Regarding 15 (Signs of destruction on buildings as they lose health are barely noticeable): I actually agree on that, just not with flames appearing without any reasonable source.