Do I seriously need to max tribe to unlock Master Mogzin??

[Brightamethyst]

You do need level 70 BLU but you don't need to beat all the Carnival fights. Just fights 25, 30, and 31.

As for which is the worst, that depends a lot on which content you do or don't usually do. For someone who's never set foot in Eureka the one that requires Hydatos access is hard. For someone who doesn't do EX trials Varis and G-Warrior are hard. For someone who hates crafting the moogle tribe and Firmament cards are hard, etc.