The canon books say the empire used the republic ships and rebels used droids, lfl and the mouse made that Canon does anyone think they won't want ffg to keep prequels stuff in those established roles?
Also what would droids give empire yet more cheap ships? We really don't need that.
But the arc and v-wing add things the empire doesn't already have, and separatist ships give rebels stuff they don't already have.
It's really the logical way to do it if it has to be done.

