Usually you want to LZ with Mew Prime T1 but depending on what Basic you start the game with 1st turn Relicanth isn't a bad alternative. You want to expand your options instead of limiting them. What most people don't get about Relicanth is that it can save your Mew's from getting donked early game while setting up with Prehistoric Wisdom thus saving for an attack from the LZ via Mew on your next turn or See Off and thus netting you a 3 card draw. The 2 retreat is bad but that's where Twins comes in to compensate for it.
80 HP on a Basic can survive one turn compared to 60 HP which is already OHKO range against Donphan and Zekrom or heck Pachirisu If setup correctly. When you're playing Mew Prime you ALWAYS want to play it safe, and even If they 2HKO or OHKO Relicanth that can also help with Twins for setting up Vileplume with Rare Candy. I would prefer Flower Shop Lady or Revive when playing MewBox, it's just too good not to run. Flower Shop for Trainer Lock and Revive for Trainer Heavy decks. You might be right on the Communications but running 4 does help especially for using Relicanth to LZ fodder something.
80 HP on a Basic can survive one turn compared to 60 HP which is already OHKO range against Donphan and Zekrom or heck Pachirisu If setup correctly. When you're playing Mew Prime you ALWAYS want to play it safe, and even If they 2HKO or OHKO Relicanth that can also help with Twins for setting up Vileplume with Rare Candy. I would prefer Flower Shop Lady or Revive when playing MewBox, it's just too good not to run. Flower Shop for Trainer Lock and Revive for Trainer Heavy decks. You might be right on the Communications but running 4 does help especially for using Relicanth to LZ fodder something.