Llamabeast: I don't think grendelkin are as good as tartarians, no. They are not as versatile or do as much for you. BUT I think that, given their stats, it seems likely that your average grendelkin with a holy scourge and maybe some other minor gear should be able to wreck 90% of all tartarians. Naked they're already good enough to kill anything resembling a reasonable level of PD. Geared they should be some of the best SC-killers in the game, despite their lack of magic. I haven't really gotten a chance to play with them much yet, aside from knocking over some independent provinces in a test game. But I can easily see them shining.
The Asynja and Cyclops are nowhere near tartarians in ability. They're capable SCs, but they have nothing on tartarians for either magic or power level. They will definitely not render tartarians obsolete.
I agree on the treelord treant comparison. Treelords suck, they serve almost no actual purpose in the game. Treants are designed to actually be useful, so of course they are better than treelords
. I also agree that treants are weaker than tartarians, though they do certainly have potential.
The ember lord may have a really high base attack, but right now it's not nearly as good as it looks like. He's losing 7 of it from lack of ambidexterity with his length 5 whip and length 2 maw. He does have a lot of attack skill though, enough so that nothing is really safe from him if that malus goes away. He's pretty comparable to tartarians I'd say, with some nice built in abilities that pretty well justify his expense. Not as good magically still, but a very good option nonetheless.
The mechanical giant is kind of meh imo. They're more or less fine... except for their magic resistance. You would have to completely load them down in mr gear for them to be usable at the current price, or else you are just asking to have them controlled away. They're also constructs, so there are plenty of nasty effects to choose from when trying to deal with them. All in all I think these are just overpriced. I think they would be better off priced similarly to the shishi (which are supremely cool by the way).
I also think the wendigo could use a bit of a price decrease, given that it takes time for it to come into power. How much of one I'm not sure. Maybe try 25 gems?
The roc is kind of an interesting one. It doesn't have great stats, but it should be enough for most PD raiding. It should also be able to kill thugs reasonably between high damage adn multiple attacks. And the siege and patrol bonuses give them useful things to do when they're not raiding. I can definitely see them being very useful. The true firebird is definitely the most niche summon. Solar brilliance can be nice, but hard to use and other than that the firebird is not that interesting in battle.