Yes, it is. And the solution should be a technical one. No merit or honor based system will work with this problem.
My suggestion: have the coders look into implementing at least a primitive autobalance plugin. It could be used at least for events where there are usually only two sides with all participating factions being allied, at least nominally.
The plugin should probably take into account numbers, IDs and fleet dispositions according to the current gameplay balance.
For example, if one side has two cruisers, and the other has none, the plugin should kick anyone logging or jumping into the system with a cruiser on an ID that can join the fleet that already has two cruisers available in the system.
Of course, there are plenty of ways to "game" a technical solution, but then the admins could step in and plug the holes that are left in the script.