Indeed, I feel it could have been good if Cadence and Starlight cooperated along side Thorax and Trixie. It could have not only have given Cadence the development she's desperately required for a fair deal of time with a grudge. It also could have kept the development that the season built up for Starlight as well. It would be interesting to see Starlight attempt to keep the peace between Cadence and some of the changeling characters, as Starlight was not only a commander in her past, but a peace keeper as well, she just went about keeping peace in a more unethical manner. Chrysalis is the same for her subjects, Cadence is somewhat similar with her abilities to spark/rekindle love. So yes, I could see how Cadence being a part of the finale would be beneficial and interesting in quite a few ways, though the idea of reformed villains against an older, still malicious villain is still just as interesting. And for the most part, I am satisfied with the finale we were presented with. Perhaps they'll dabble with a similar idea later, with Queen Chrysalis still roaming free.