But this is avoiding the elephant in the room that is tartarians with a shroud are very cheap for the power you get. Especially when the counters will be 1 time use due to blood vengeance. Factoring a rather generous 25% of them will effectively be useless puts it at an average cost of 13 gems per usable tart, add onto 1 of the tarts is a flying man eater with only a helm slot bumps it up to 15 death gems per thugable tartarian. Throw on a shround for 5 astral gems, so 20 gems. That is still insanely strong for the cost.
Incidentally, I think you should really spend a bit of time in Debug Mod; TG is not half the spell you think it is, and/or are being told it is by guides that never got over Dom3. 5m in Debug Mod got me 100 casts of TG. 77 of the 100 were non-commanders. Of the commanders, 21 had body slots, 20 weren't injured to the point of being animate walls, and 8 weren't Feebleminded. Don't forget, Feeblemind gives the gift that keeps on giving, which is to say -5 MR. But even if we count the MR 13 tarts as equal to the MR 18s, on average you're going to be spending ~50 gems to get one that's out-of-the-box thuggable by the criteria you laid out - plus 5 gems for the shroud. At that point, you're better off going with GoR/DN if you have access and with THAT assumption, we still only have a 75% level of usability [(6/7 has-bodies) * (7/8 not-useless-broken)]. So it's an average of 13d + 20n + 5s or 13d + 30s - and at that level of investment, I'm not overly keen on sending out a Feebleminded present to my enemies, so let's rule those out, even though it makes it even worse. So [(6/7 has-bodies) * (1/3 has-brains)] gives us ~35d + 20n + 5s or ~35d + 30s, plus 6 mage-turns - 4 of which are D7.
This is not an amount any sane person would be spending for a thug.
Even before we consider the other half of this which I don't want to get into because it'd be doing you job of beating me for you, your fears are vastly overstated.