I guess you misread my statement (even the part you did quote).
Read again... Unless you consider Pyre Zombies to be adepts/mages... (which fill a simmilar role as Sieges in FFH2 but are much better in many ways, Pyre Zombies fill other Roles as well, and decently so. Thats whats their strength.)
Hint for better understanding (given the message is a given a bit unclear, but clear enough to be seen if read thoroughly):
My comment was mainly aimed at the "siege-units are just assasin-fooder..." part + that Pyre Zombies are not the only way to go for Sheaim (or only threat the AI fields while playing them since they sometimes bring on quite a number of death 1-adepts if they survive beeing rushed by me
and others.)... + that an early huge AI stack of siege units (most likely seen in form of trebs with a few dwarven meelee units for support and possibly quite earlier than zombies) can pose a simmilar (if not all as big of a) problem with simmilar counters necessary... (And that assasins are far from a really adequate counter. For many reasons.)
Since this is a strategy and tips forum those statements (like siege=just assasin foodder) should be evaluated as well imo and not ignore if they are just plain wrong.
Lest unexperienced players reading it here really try to counter a stack of sieges (backed up by a few other units, most likely beeing melee) with a smaller stack of assasins (you can imagine the outcome...).
Most of your points i did as well even though in a more general and much shorter way (since i consider them more or less obvious, even to rather inexperienced players unlike sieges immunity to poison-damage), but explicit enough to be a clear statement of not! siege>pyre zombies. Doesn't change that an early (AI) superstack of sieges can pose a simmilar problem as well (had it once from cassiel at early Tier 2 / the time i had Axemen at Deity. Annoying to boot.). Or whould you disagree?
I don't like siege very much in FFH 2 but its a tad bit better than sometimes made out to be.
Its still a very early and relatively reliable (85% Withdrawl is enough to call em that.) stack buster + city cracker. (and from top of my head with anyone but luchirp i whouldn't get construction and thus normal catapults, much early anyways so they are not of interest anyways since from Late Tier 2- early Tier 3 Melee / Recon / Mounted or Tier 2 Divine / Arcane there are much better options available usually. Trebs sound sorts of neat even at that point, if a bit to slow for my tastes.) siege bashing is a bit! overdone imo.
Their biggest problem that those things are lacking any mobility.
But if huge Stacks containing a few or even lots of them appear early, they still are bloody annoying.
+ theoretical costs are rather inconsequential when you face such a stack in the field, aren't they?
And just in case my english should be broken in that regard (quite possible), the cost-comparison was between assasins and siege of course...