Tartarians are frequently too broken to be terribly useful as more than giant super-chaff if you don't have GoH, which is the only way to heal them. They're also frequently in need of GoR/DN to make them into commanders even if they're not broken (with Feeblemind being a particular favorite break) and if you want to use them as SCs. After you've sunk an extra 25 gems into them to give them slots, you need to kit them out or they're just very robust mages that can be fairly easily targeted with "Attack Large Monsters" or by relying on their large HP pools to attract evocations. Once you've sunk another 10-30 gems into their gear to SC with them, you're looking at 50-80 gems for someone who's possibly walking injured, and has Shattered Soul 25 (which is not mere insanity), and is still just a single unit vulnerable to all the counters that (large) single units suffer from. Trust me, they're nice in a niche, but this isn't Dom3. And they're also just as much a threat from C'tis or Agartha as me (which is to say, not much of one and not for several handfuls of turns even then) - for that matter, both of those two can more easily use the Jade Mask than I can, and if you wanna churn out D7 spells, boosters matter (especially if you don't have a high-D pretender like, hmm, would that be me?).
Being next to any good player with a decent nation is game over for you unless you can overcome them. Trust me when I say you're next to a number of good players with decent nations. Ermor has some risk/reward issues which slant perceptions of people wanting to attack them, but they're not actually more devastating than a number of the nations our game is blessed with if left unmolested... and a couple of those seem to be right now, heh. This rep and "conventional wisdom" leads to the perpetuation of more conventional wisdom about how Ermor is the greatest threat in any game it's in. It might be or it might not. It's silly, albeit convenient, to believe it always is.
Finally: the venerable "win rate" polls don't tell as much as they're often made out to. They're self-reporting, and unless the methodology has changed drastically, there's no controls for overlap. They're also drawn from significantly more FFA/low diplo metas than ours. There's also no control for whether someone good played a nation or a neophyte... though between Ermor's rep for getting piled on and its micro, it's more likely to scare off inexperienced players with no overarching plan than most nations. So again, don't read too much into those numbers. They're an excellent example of statistics that look to show far more than than they can even begin to hope to...