Murloc Paladin is just a braindead highroll aggro deck. I don't know how it's doing so well when pretty much every board clear in existence totally bones it.
First of all it is favoured against Mage (which makes up 20% of the meta at legend and 15% at lower ranks) - it generates early pressure with Murlocs, which Mage is weak against. If it lucks an on curve Lens > TTS, Mage's 6/7 cost AoEs are not yet online to deal with it without Doomsayer leading into the Paladin's turn 5 (or 4 on coin). The Paladin deck is likely to deal critical chip damage with the first wave of Murlocs, and then it plays Leeroy, Zephrys and Chef Nomi to finish the game.
Secondly the deck is countered by L2P, which always promotes a high win rate in the early days. Players at higher ranks understand that you don't have to concede to a Lens > TTS on curve, and also have a clearer understanding of how to play their early game out in order to maximise their potential to trade off as much of the board as possible and minimise the early damage they take. At lower ranks however, there will be a lot of people conceding instantly when the TTS comes down because they either didn't set up for it correctly or simply don't believe they can beat it. The mulligan win rate of Lens is 66% and the played win rate of TTS is 59%, and I'll be shocked if these numbers are not hyper inflated by a huge amount of rage concedes.
The deck is pretty good, don't get me wrong, but its win rate will decline RAPIDLY when strategies against it become better known further down the ladder.
I dunno I was beating murloc paladin with quest druid and secret mage. I imagine Highlander mage probably walks all over it too. Maybe it's just favored against the super greedy conjure mage lists. You're probabaly right about the rage concedes though