[PvK]

If you made some very-high-tech killer drones which use a lot of supplies, then you could have something to discourage fleet accumulations, because an expensive drone attack could threaten a fleet concentration, but would not be cost-efficient against moderate-sized fleets, because it would only be good for one battle (thanks to a high supply use - perhaps high supply use to move from sector to sector, which would eliminate the drone if it moved). Needs refinement and balancing, but perhaps it could address the mass fleet issue.

PvK