@Aaron-Patten It's not that Blue is any more a threat than anything else. It's just that, given the enormous power level of the core Blue cards that you run in Vintage, anything you print on that level just gets run along side them. Let's say they printed a black spell that did something horribly broken like, I dunno, regrow your entire graveyard. That would just get slotted in right next to the existing blue shells, don't you think? (P.S. Yes, this is a joke. )
Dredge and Shops are awesome because they are fundamentally incompatible with the Blue spells. I mean, sure, sometimes you see someone jam blue in a shops or dredge list, but not often and (usually) not successfully. They represent a way to play Vintage on a whole different axis.
Bottom line: they lead to a more fundamental form of format diversity than we would see if every deck started with half of its cards determined by the Reserve List. I'm sure a lot of people would enjoy the Oath v. Storm v. Tezz v. Mentor metagame. But, it feels elitist for people to say that there should be no other options.
I just want to point out that, right before Chalice of the Void's restriction, everybody was also saying that the Vintage metagame was the most healthy they've ever seen. So what is it? Now or before CotV?
Why can't it be both? I think the meta was great before and after precisely because hitting Chalice didn't cripple shops. It just shifted it around a bit.
Now, it DID cripple hatebear.dec, but that's another grumbly story...