Well, I agree that you can have a successful hatch without a weasel/weiner/wiggler thing in the bator just like you said, by keeping the temps correct for either the still air or the circulated air. Sometimes, with a full bator, it's hard to get that thing situated in a good spot anyway.
I do use one, if I have room, but I still think it helps at least the first time, to have it so you know and can see for yourself that small temp fluctuations dont hurt the egg as much as you'd think, that the interior of an egg takes the temp changes slower than the bator air. And you are right, that it could become a crutch, but then, if it makes the operator feel better and there's room, why not? You should get to know the bator, definitely-where the cool spots are, etc.