2) Disallow the Stacking of Certain Debuffs/Effects (Or Re-Implement Unique Immunity)
This is quite possibly one of the most broken things possible in Frontline. It is painfully clear many of these types of abilities were never meant to be used back-to-back since you would normally only encounter just 1 of them every CD window in Crystalline Conflict. The biggest offenders are Miracle of Nature, Reaper's Limit Break Tenebrae Lemurum with its Hysteria effect, and Dancer's Limit Break Contradance with its charm effect.
With Miracle of Nature, if you have enough WHM on a side and with proper focus/coordination, it is possible to fully shut down a player or players for an extended period of time that is just simply broken. For all other types of normal crowd control, you can use purify to give yourself a window, but it does not work against Miracle of Nature. This is fine in theory for a single use, but not for multiple uses in a short time frame. This type of chain use was never the intent of the ability since it is designed around a mode where there should only ever be 1 WHM on each team with a 45s CD window. Thus, this problem does not exist in normal Crystalline Conflict play. Yet in Frontline, it's possible to keep a RPR or WAR locked out from anything other than movement for the entire duration of their own Limit Breaks, which are critical parts of their toolkit. Stacking oGCD abilities should not be able to fully negate a Limit Break (IMO, you should have to spend an LB to counter an LB). Simply adding a specific Miracle of Nature resilience that lasts 45 seconds would solve this issue.
As for the more important issue of certain Limit Breaks, getting hit by multiple DNC LBs to keep you locked out of actions for longer than the duration of a single DNC LB should not be possible. Same with RPR and WAR LBs. Similarly, MNK LB should also only go through a single guard + stun. A 2nd MNK LB, while it should deliver damage, within a certain window of time should not break guard or restrict your movement. The window of time is up for debate, but I'd start with a 10 second resilience to each LBs effect. However, using different, unique job LBs in succession would still be possible, so using 1 DNC LB, then using 1 RPR LB, and then 1 WAR LB, etc, etc, would still work. But no more getting chained by multiple DNC LBs or locked down by multiple MNK LBs. And again, like I said in my first bullet point, any AOE LBs should only affect up to 5 targets max.