I believe the rational for no fighters in the Trek Universe is that the larger capital ships have higher warp potential than the smaller craft, there seems to be economies of scale that allow those large ships to reach those higher warp numbers than is possible for smaller craft.
I just had two realizations:
The first: shuttle Cochrane
, from everyone's favorite apocryphal VOY episode Threshold
, was able to reach Warp 10 (even if you don't accept that, it did reach a warp speed beyond what Voyager was able to achieve). Likewise, the Delta Flyer could reach high warp velocities. These ships could even be outfitted with transwarp and slipstream drives, which probably require even more energy than traditional warp. I think the available data is contradictory as far as how small a M/AM plant can be made.
The second: If you're going to have fighters, you might not even need them to be warp capable at all; even if they were, you wouldn't need to ever be more than 24 hours away from the mothership. Fighters would be deployed from a carrier ship, likely heavily armored/weaponized itself. This carrier would have warp capabilities, and could deploy the independent fighters into a battle. Not very many battles (a few) depicted in Trek were at warp speed, most are at impulse. A maneuverable fighter would be tactically superior to a massive ship that is much slower to turn on a dime.
Several such ships were seen in VOY Drive
, although these were all two-seaters. Even though the Delta Flyer had a warp drive, the race was required to be conducted at sublight speeds.