Copy and paste second alliance-locked campaign.
Make it Gray Host 1 and Gray Host 2 for testing.
Gray Host 1 will be with group option enabled.
Gray Host 2 will be with group option disabled.
Make it run like that for a month and collect statistics.
After that,
leave the campaign with higher average population running with higher server HW resource allocation.
leave the campaign with smaller average population running with smaller server HW resource allocation.
Anybody who wants to play grouped will have own Cyrodiil.
Anybody who wants to play without annoying and game-breaking groups will have own Cyrodiil too.
Splitting grouped and non-grouped Cyrodiil would also greatly help with overall performance and latency.
The same way like we have CP and no-CP, players should have option for grouped and non-grouped Cyro.
You normal players trying to play Cyrodiil and have fun, you make of 95% population. Ball groups are about 5%.
You are allowed to have fun too and you don't need to be group food for hours every single day.
It would just mean no PUG's, because you wouldn't like to play PUG in a ball-group Cyrodiil.
You have /z and /y and /s anyway, no need for groups.