I'm not sure it's clear cut to rank Dredge hate. There are a million answers to Containment Priest, but at Eternal Weekend and leading up to it, many Dredge players cut them, plenty having zero answers to the card. The Hollow One/Gurmag Angler package takes up space. Good Dredge players are constantly adapting their answers to line up with popular hate strategies, which means good players of all decks need to adjust accordingly.
The best hate card isn't Leyline of the Void, it's whatever's one step ahead this week.
I certainly can't speak for every Dredge player. But I can say that in my experience, learning to free yourself from the fear of GY hate has been crucial to becoming more proficient with the deck.
A newer, or less-experienced Dredge pilot is going to see 4 copies of Grafdigger's Cage, and 2 copies of Containment Priest in someone's SB, and think 'What am I gonna do?' That's going to hinder you, or give you pause, and that feeling is going to stick with you in your post-SB games.
But if you can form that hierarchy in your mind, and go, 'OK. I have 4 Gurmag Angler, and 4 Hollow One. I don't care about of any of those cards,' that frees you from the fear, and should effectively help you play better.
Likewise, I think that people who pack those cards count on us backing down, or feeling defeated at the sight of them. But I don't really flinch when I see a Tormod's Crypt, because I know on my hierarchy of things I care about, it's not too far up there. If you pop the Crypt, I can always rebuild. I'm not giving into that fear that you want me to have of that card.
Maybe this is why my record with Dredge is so abysmal. I don't get discouraged right away though, usually after the beats get progressively bad over a few turns.