Fighters are pretty effective from my experience, though that is outside of the TSN mod. They just can’t stand up long to oncoming fire, but if their mothership can take the brunt of the punishment then the additional firepower is quite noticeable. A fighter or two can also be left to engage smaller fleets while the mothership engages heavier targets.
All of this assumes that you have enough warm bodies to fill every position, and I agree that most people would prefer (more ships/no fighters) to (fewer ships/a few fighters). This is even before considering that converting fighters to shuttles gives greater RP opportunity rather than having a cruiser loitering near a station waiting for the Comms message that the transfer has been completed. If people really want fighters for simulations, some fighter enabled duplicates can be tagged as “Ximni” vessels rather than TSN, even if they otherwise look and function like their TSN counterparts, but would carry combat-oriented fighters.