So when is AST getting nerfed in Frontline

[Scintilla]

Premades aren't actually an issue. I just got out of a seal rock game that had Flames win while being over 600 points ahead of second place. Did they have a premade? Yes, probably. Were they the issue? No. What was the issue? Every time they went for a DRK pull, at least half the people on my time refused to press Guard, and they got deleted. No, they weren't throwing WAR/DNC/RPR limit break into it. Premades are not the issue. Rather, they highlight the real issue: people cannot be trusted to use their 90% damage mitigation cooldown.

If you're only saying it was 'probably' a premade, then it clearly wasn't a particularly good one.

I spend the majority of my online time in frontlines and about the only role I don't play in them is ranged. Yes, in random teams a sizable proportion of the players will be playing purely for roulette. They may take little interest in the game, just want it over with as quickly as possible, and probably wouldn't think to use Guard: they were full HP one second, dead the next.
But even amongst the players who do use it, whilst Guard may save you against many smaller or less coordinated premades, in some cases even that isn't remotely enough. Against some teams, even using Guard can leave you almost instantly deleted - it just buys you maybe an extra second, making you one of the last of your team to be so.

When it becomes clear we're vs a premade all you can really do is try to avoid grouping together too much (almost impossible in some areas, such as Fields of Glory and the centre section of Onsal Hakair), mark the DRK, use Guard if you do get caught. Focus them down and hope that the other random team does the same. I suppose some classes can help somewhat: AST and PLD for heals/defence and perhaps MNK or MCH to try to push away the DRK when they see them coming to buy a little time.