Well, with all due respect, it seems your maths is wrong. If you use Cahir, then you lose one other card from the golds (there are only 4 spots). Counting decoy, we still are at 10 cards milled. So, that means you need 2 tutor cards for a mill to get you to zero cards in 25 cards deck. To get mill an advantage, you need more tutors than that. That is, obviously with the perfect draw in the mill deck, which happen rarely, as mill deck normally does not thin to zero, but have 3-4 cards left (with all the card drawing cards played - if one has 1 of those cards in those not drawn cards, mill player cannot draw all those cards, leading to failure at milling and easy loss - typically at least 1 drawing card is not drawn - they are many).
Now, small hints - if you see mill, do not play your spy... discard it instead... Also, if you expect mill, play your cards smartly, so Sweers will get max 1 card (or zero) - you know, Sweers has to be played before any cards which cause card draw, so there is quite a bit of guessing the mill player has to do. Some folks call it skill, but it is mainly skill of the opponent as you give targets.
Finally, yes, if you use the ST dorfs, and *if* mill player has the right cards, mill is favoured (but not as much as you think in case of expert players). It is highly favoured, if you do not play really well in the round 2 (you should be getting rid of your tutor cards in that round), do not play around Sweers well and perhaps make an mistake with playing an extra spy with summoning circle if you run that card. But honestly, you can have 25 card list and win with mill 30-40% of time. If you think mill is a problem, you can also easily use 27 cards in that deck and the mill player is dead in the water, while your deck is just very slightly less consistent. With 27 cards you will win with mill archetype every single time - of course at a cost of losing a little bit more often with some decks which are thinning more aggressively.
Finally, I do not think that any deck should thin to zero cards without any help from the opponent - which is now the case for some popular decks. Those decks are unhealthy as when you play against them, it is almost always the same game, which is not that great - and as those decks are similar - it is getting boring very quickly. That is the case why ST dorfs are disliked - not only the deck thins efficiently, leading to you seeing the same cards (well, almost the whole deck) again and again, but additionally it is not very interactive - the ST just build their side of the board, with little regards to opponent actions and not much interactivity. So, there is not that much of meaningful stuff the opponent can do while playing, apart of the same standard actions, as there is little uncertainty about all the cards being played... On the other hand, when playing against decks which do not thin so much, one can hypothetise which cards the opponent has, which are in the deck and try to adjust strategy accordingly - uniquely in every game.