Based on what I collected before, Dredge was killing at 27% by the end of turn 2, and 60% by turn 3. Effectively would be less than that. So Dredge "effectively" decides its games very quickly.
I'm a little skeptical about that. Most Dredge lists I've seen recently did not have a Dread Return target that gave haste or did direct damage, so the Turn 2 kill % should be zero for such lists.
None of the lists on Goldfish's metagame right now have a haste or direct damage target: https://www.mtggoldfish.com/archetype/vintage-wubg-96200#paper
Even if you're right that Dredge is "effectively" killing on a very early turn (which I think is a fair claim if you're just saying in an abstract way that Dredge is faster than most blue control decks), I think Dredge is scoring kills more slowly than it typically has in the past, which raises the question of why a restriction due to speed would take place now.
These decklists pass the turn at the end of turn 2 with a ton of zombies in play and a hellbent opponent. Dread Return might make the game physically end sooner, but it’s virtually over against a majority of decks if they haven’t interacted with, or killed you before your turn 2/3.