Caveat all of this with the fact that I thought Fire was hands-down the best option for me. Also I'm going to assume level 10 evolutions, since you mentioned portal profits. I'm also going to assume this is for people fairly well into guest races (say Woodelves and onward), since you mention the desirability of portal profits (which I consider wasted on races like Dwarves and Fairies - they're already easy enough).
But I don't think the bases are very overpowered. First, all 3 give similar amounts of gold, and no one cares that much about gold. The supplies are nice, but not unique to Fire. The broken shard is only useful at times, and honestly most people fighting in tournaments a lot are always at the 10 shard cap. So it really comes down to the portal profit. Which is awesome. No disputing that. But its also a reward that requires basically all of your event currency to achieve, and 16 squares. And its equivalent to 7 Trading Outposts. Which are not that hard to come by.
I think Fire can be overpowered with the right synergy of certain wonders. But its really only overpowered when its being fed. But the battle one needs to be 24 hours, otherwise it would be relatively useless for tournaments (and I think tournaments are its primary applicability - more later). You would only get to use pet food for 1 round of fighting if it was a short timer, like 3 or 4 hours. No one is spending the relics and MA academy time on pet food for 1 round of fighting at 50% boost. Its just not worth it.
Now, if you have Timewarp, and you can cram 3 rounds of fighting into 24 hours, the buff becomes great. But that also means 1. you're done with Constructs (not applicable for most) and 2. you devote 2000 or so KP into an AW. You can also get great value by scouting for 2 weeks or so (not clearing though), then fighting all those provinces at once. Of course there's a downside of opportunity cost (e.g. 2 weeks of not getting the expansions, KP, relics that those cleared provinces will give). So even then its not "overpowered."
I think the base rewards for Aureate and Storm are solid, especially at level 10. I like to think of those tier 1 goods from Aureate less as goods, and more as free population. Because now I can probably delete a tier 1 factory. Storm is also a lot of mana, and everyone loves KP. I'm down a bit on mana, because when you're in between chapters, there's really no use for mana. But that's true for very few players.
As for the feeding rewards, I haven't done the math. But I'd think certain playstyles (i.e. lots of factories) really benefit. But even if not, I'd think if you time your feedings appropriately (i.e., feed right before collecting a 9hr production, while having MM spells up, then immediately running a 3hr production) you can get close to replacing a factory. And again, that basically means that you save population anywhere between 2K at low levels to 14K at higher levels. But you're right. If you only log on once per day, or if you log on 3 times per day, but with 7 hours in between, its hard to use Storm or Aureate well.
Also, flip around the population analysis and think about what that extra 5-10% (madeup numbers) of goods can get you each week in a tournament in catering. If you can take 3-4 more provinces to round 2, that's another 15-20KP (plus other benefits of tourney participation). Or maybe it pushes your fellowship from chest 4 to chest 5, and then your whole FS is getting 25X more rewards. And if everyone in your FS takes this approach, maybe its everyone doing more in the tourney, and now maybe you're at 7 chests.