MA Ctis feel may be very right, it may be OK for turtling in early game, but consider that
1) You have GREAT difficulties diversifying your magics. Most indie mages die in your dominion, so you have to provide them with rings of regen every time.
2) Your mages cant craft some of the most important items, so you cant really equip thugs or SCs.
3) You have bad battlemages. Dont even say 'sceleton spam', its too Domionion II. With 40 fatique per cast, marchmasters cant raise enough skellies.
4) You have problems getting half-decent SCs until you get to summon Tartarians. Raiders, yes. SCs - I dont think so. Also, see part 2 of my list.
5) Turtling only works early. Granted, you wont be a target of priority... but then armies get more expendable, and that disease effect kills really slowly. I played MA tis, I know. Of two really BIG (300+ units) armies that invaded my lands, hardly a single soldier died because of disease.
Now, the pros... Clamming. Thats it, I think.
P.S.
We'll see the outcome of your little struggle against Tien Chi. I think its going to illustrate my points better than words.
P.P.S.
Back to the topic - poison immunity doesnt help against disease. Regeneration helps staying alive, but doesnt prevent catching disease. That much I've tested.