Hey,
I play imperial on Kinrath Spider and I've only ever seen ~180 max at imperial fleet. Generally our leveling zones have 30-200 people in each. So although there are more imperials on the server, I think that the server cap has a lot to do with ho many players you're seeing. That combined with the faction imbalance.
Our server during prime time is "FULL" yet there's never more than 2 shards present on any planet ever. (2 being rare)