This seems actually more RNG dependent than rag vs nef, going first is probably a huge advantage in every single match up.
Disagree unless you get Alex in hand.
Against Priest, going 1st is usually pretty bad because what's going to happen is that they will just Mind Control your opening big creature. From there you basically just lost the game.
Going 2nd you can generally do pretty well as long as you mulligan for one premium removal. And for Rogue going 2nd is still preferable because of the coin with Gadgetan (they really don't care if you play a big Legendary unless its Alex).
The meta is simply that if you are going turn 1, you mulligan for your best drop (usually Alex) and if you are going 2nd you mulligan for you removal + a slightly smaller creature. So Rogues can do something like Sabotage + Emperor or Sabotage + Gadgetan or they can do Sap + Ragnaros.
Really though the main breaking point of this Brawl is Alexstrasza. I have played games where I have come back from turn 1 Alex (usually BGH into Dr Balanced tempo play) or had my turn 1 Alex come back from but it's just way too easy to get turn 2-3 wins with turn 1 Alex. Any class can do it.
Oh and Arcane Golem and Faceless are really cheesy in this format too. Mostly because classes generally have 5 or less removal so they will first Faceless your big Legendary and then remove it which will result in you being ahead.
This format basically just showed how broken Gadgetan would've been at 5 cost. Even in this format it's super broken and can win you game from the first turn. Not just Rogue but Shaman can abuse it too.
Still this Brawl results in fast game and lots of big Legendaries to get used a lot. I got my fastest 7 win quest with this Brawl using Miracle Rogue.