Temperature scale isn't
all good. Every pick the temperature differs from your nation's preferred, you lose income, resources and supplies. Unless you have strong dominion, seasons effect this. Unless your dominions spreads very fast, you'll have to preach in conquered provinces before they are in your preferred temperature, and then wait until they catch up with the warmth.
The nations that need spesific temperature need high dominion, possibly with a special theme improving dominion /temperature spread.
Also, some nations require less resources. E.g. Mictlan can survive with Sloth 2 or 3 AND use its many national units (mainly Jaguar Warriors, of course). Jotunheim can't, especially not Niefelheim. Pythium starts with
7 gems, and has
free communion slaves. The thing is, many of the nations have something special, something that makes them worth it.
It's also often the case of
how you play, as well. I don't remember how Gandalf used to say it, but the nations are just tools which the player must use. A player must choose a correct tool for a spesific strategy, and e.g. Pangaea can be deadly stealth nation. Gandalf has these wonderful stories of Pangaea scouting provinces with the Black Harpies, then conquering a province via Call of the Wild with (possibly) some stealth support, then building a castle, lab, temple with the stealthy commanders - and when your enemy finds your "capital", he'll be
very confused!
EDIT: you don't recruit provinces...