Drox 2 empires could use some order of battle variety perhaps?
1. a "boss unit":
a. when they reach four planets, a boss unit emerges
b. this ship is a class or two sizes larger and is decent, but not quite as strong as "average" boss monsters, and certain not in the league with Bounty Hunters, or Drox Operative ships.
2. a second concurrent active "ship class": i.e. Brunt ships could have two different types of missile cruisers (one EMP, one swarm), or Drakk get a few ships with fighter squadrons to mix in with their normal line ships.
3. Some variance in the ship sizes for each empire: i.e. a random chance of 1-2 hull size variance for each ship (the empires should still field equal weight of ships on average). I.e. I found it strange that an entire race's fleet were all identical ships...