Title. Ever since the 6.1 rework, the nature of FL has been to find the most meta job and stack as many of those as possible. This is typically a job with an AoE ability that is easy to use in consort with others to wipe entire teams and build Battle High quicker. We have seen this in many variations. SMN, DRK, DRG, WHM, SCH, AST have all been known to job stack.
While this is not technically cheating - these players are simply playing the jobs available for them - it points to the number one issue with Frontlines. It takes what is supposed to be a form of casual content in which you are allowed and encouraged to play with friends on whatever job you prefer, but makes it open to abuses such as job stacking. While I agree that friends should be able to queue together, I do not think 4-man job stacks should be rewarded for playing all four of the same job to gain an unfair advantage on the enemy teams.
The consequences of this are far reaching. It discourages solo players, people with schedules that don't allow them to play FL frequently, or people without friends to team up with. It prevents players from reaching achievements in game when they are unknowingly teamed up against a pre-made job stack. It destroys the casual nature of Frontlines, compelling players to play meta jobs instead of what they enjoy. And it unjustly rewards players who are able to transform their higher-than-average win-rates due to job-stacking into Gil making.
The solution, unlike the blanket nerf to Summoners following 6.1, is we need a dynamic system in place that discourages job stacking when it takes place. We should not disallow it completely, nor should we prevent friends from queuing together. After all, this is meant to be casual content. However, if duplicate jobs are not allowed in Crystal Conflict, and duplicate jobs slow LB generation in PvE content, then an equivalent consequence should be added to Frontlines.
My proposal: if 3 or more of the same job is present on the same team, then all three take a massive dmg reduction represented by a Damage Down debuff on their bar that remains until one of them changes to a separate job. This Damage Down debuff escalates in severity as more people stack the same job within the same alliance. Between 19 jobs and 24 slots, this will encourage a far more diverse array of jobs in FL to avoid the Damage Reduction. Players will be actively encouraged to play their favorite job even if it isn't considered meta and will arguably have a better effect on job-stacking teams rather than blanket damage nerfs to whole jobs. This proposal is designed to be dynamic, changing to each unique match as team comps change. And perhaps, also, players will be encouraged to try out new jobs in Frontlines that they normally would not have considered playing.