I just checked Steam and the rarest thing in Civ V is losing the Korean scenario as Korea. I never played scenarios much until Civ V. I spent some time trying to earn badges, but some of the scenarios so change the game that my carefully developed strategies don't apply.
I think some badges are much more difficult to earn, but badges for losing a scenario a certain way... Why would I want to accomplish that?
I was playing as Spain as I'm half heartedly trying to win with most Civs, and noticed you can have Frigates before you invent cannon, yet my Frigate clearly shoots cannons... I think you can even research the tech that lets you build Frigates without discovering Iron Working...
Worst of all it appears you can build a castle without discovering the Engineering tech. I know the expansion is going to adjust the tech tree some. And I know it is a game and design decisions are made for playability and profitability but there are definitely oddities in Civ V.
I've build the odd Iron Clad though I agree they aren't great, on the right map they make sense. Someone on another thread about Unique Units commented that defensive unique units will always lose popularity contests. And it is true I think most Civ players play much more aggressively than myself and resort to war as their first, primary, and only strategy. Consequently units, techs, and Civs that are defensive or need a longer time to become powerful are devalued.
My biggest untested theory in Civ is that map size would make certain civs more powerful say Spain or England or America and due to real world time and processing power constraints. Your civilization preference isn't just based on tactics but map size and thus game settings. Civ will never become a spectator sport game, though people watch chess so who knows... Perhaps on larger maps defending your continent becomes more of a necessity and coastal defense boats, which is what the Ironclad is in Civilization V become a valued commodity.
They require Iron and many other things require Iron so most people would rather have Trebuchets and Long Swordsman and probably prioritized their research to get those techs, using up what little iron they have providing a disincentive to research and build ironclads.
I also think their is a subset of Civ players that always play Pangaea maps and don't want to waste time research naval tech and building naval units.
Steam does give the game designer a lot of information they can use to refine the game, rather than just relying on the most talkative folks online.