>>42306305
>>Pinkie is usually an instigator for plot and relationship purposes which is spurred on by her profound retardation, she's the most "important" of the bottom bitches but there's a power gap between her and the normal ones
Yeah Pinkie is more of a catalyst/enabler of differing plots rather than a major player.
Twilight has always been at the forefront, and Rarity and Rainbow have both been getting more and more relevant and important with each new episode/movie.
Plus it helps that they are aesthetically pleasing when standing next to each other.