Well they are wrong... Anyway.
-2 Trag. It isn't as relevant, especially when hardcore "no special summon" and Evilswarms are in your face all the time.
-1 Allure, since we are going to take out the trags. Yes after undine controllers are dead draws, but you don't want to go into allure as much rather than other cards I will discuss later.
Keep Undine at 3. There a reason why its called "Undine mermails". Also in matchups such as "Vanity" and "Evilswarm" Undine gives you more options, increases consistency and gives you more outs.
+1 Infant, with more matchups where you need to get rid of monsters infant is relevant at 3 now.
+1 Abysspike. You need more outs along with undine with Evilswarm and speed to get rid of monsters such as big eye, and gaios when playing against the newer meta.
+1 Crimson Blader : This card alone pulled off instantly can win you the game against E-dragons.
+1 Bahamut Shark
(That leaves you choice to add a lv 8 synchro I would use stardust.
+1 Abyss-Sphere. Spere is always at 3 in a mermail deck. It opens options, and gives you better set-up and can lead to disrupting your opponent's plays during the BP and when they are going to end their turn.