Its been talked about before, but citizen soldiers are quite fundamental to 0ad.
There's a big discussion here:
Citizen soldiers allow for big battles that distinguish 0ad from aoe2, and they are quite historically accurate which is something 0ad strives to achieve. That being said, they contribute to snowballing, and mainly contribute to the "booming = turtling" phenomenon.
I would like to not abandon citizen soldiers entirely, as it makes 0ad unique, but we can increase the importance of non-soldier gatherers by changing gather rates and/or by introducing a new "laborer" unit.