Chaggie in the pilot balance each other out without it feeling one sided. Charlie's warm, calm-collected, reassuring nature complements Vaggie's hot headed aggressive impulse, with Vaggie's level headed orderly outlook complements Charlie's hope-ridden optimism.
Series Charlie is all the emotion in the relationship, and Vaggie's a straight man.
Pilot Vaggie not sharing Charlie's musical fantasy might be because she herself isn't much of a singer, but rather, have dancing as her forte. The comics from the original episode list has Vaggie impress CarMax with her dancing skills, earning her respect.
Not only is Series Vaggie a dancer (well according to her audition sheet/Playbill section), it turns out she sings too! So while Charlie's a singer, Vaggie's a singer AND a dancer.
To reiterate Chaggie worked better in the pilot because the two were more multidimensional in terms of surface level characterization and had traits that were unique to them, which in turn, could venture in dynamics with others, partially resulting people pairing them in different ships. Their personalities in the Series were limited severely, so they come off as dull as it seems like they were only made for each other, so people are hyper focused on the relationship as it seems like that's all they have.