They stated in the explanation that they expect Midrange Paladin to rise a lot after the nerf. They also expect Mage to rise a lot because Paladin will rise and they expect Mage will be strong as the counter to the class.
Also this snapshot is what it looks like right now not what it will look after the Patron nerf... otherwise Patron wouldn't occupy the best deck slot.
It does, but specifially under the aggro druid it says
"When the Warsong Commander patch goes live expect to see a rise in Secret Paladin, a favorable match-up for Aggro Druid, which will make this deck even more powerful."
But nothing about midrange, and it has the matchup at 50/50. Under midrange it says
"As Patron sees its last week on the ladder, we expect to see a fair bit of it, but aside from the Patron match-up we see Mid-Range Paladin being a very strong deck. It beats Aggro Druid with ease; you can keep up with its early game, deal with Fel Reavers without an issue, and heal when needed."
...yet also has it as a 50/50 when it isn't. It's like it says that but wasn't really considered in the rank.
There's certainly going to be a lot happening with stuff like mage rising like you said, but this specific thing seems weirdly done.
Druid can just silence the reaver, go back to an 8/8 with no downside
It's true that they have double keeper for this, but from my experience the deck doesn't tend to have many cards in hand and that isn't a card they would keep in the mulligan phase. Though even in those instances, pally also runs BGH and equality which handle it. From what I've seen the match isn't even close since pally also can have super aggressive starts.