Discrepancy in lore (spoilers)

[Bhearil]

That doesnt work when you have literally an army chasing you or battles would be won by a single mage casting grease and making the enemy army slip and keep falling. She probably used some tricks to earn some time but there were literally too many soldiers, plus we dont really know the extent of her powers on that moment, and in any case those tactics doesnt make you inmune to ranged atacks (actually Thancred got an arrow to the knee if remember well).

Also if she would have frozen a larger area of water would have meant they would have been caught as well, their legs trapped in frozen ice. That mages due yo gameplay reasons cant eat their own spells doesnt mean that lore wise on confined spaces wide area of effect effects arent nasty. Either the effect is too small and thus irrelevant outside of trying to get extra distance, or is too big and they got caught in it since they were on a tunnel.

Many DMs will grin when some player has the "brilliant" idea of using aoe spells in closed spaces and kill half of their own party alongside themselves

[Vyrerus]

That doesnt work

Blizzard 1 used to inflict Heavy and Blizzard II used to inflict bind. Blizzard II was a cross class spell for both healers back then, and she's powerful enough to cast a spell that brings down the tunnel they are in that makes use of wind, earth, and water elements, then she is powerful enough to freeze the water in front of her. Keep in mind she also simulcasted a forbidden teleportation magick.

That wouldn't have made for as dramatic of an ending with lots of ways to write the after effects. It makes her seem dumb though.

As far as you saying it wouldn't work though... uhm, you're underestimating the effect of terrain on movement. Quite regularly there is a floor mechanic in fights where the floor freezes and players have to slide. It's called thin ice. Quite often, we as players slide the wrong way. Your movement gets locked in, and you often wind up in a bad spot. Single mages don't win wars by this, because there are obviously mages on the other side to counter.

They didn't have a whole army chasing them, just the Crystal Braves and the Brass Blades. Not in their entirety either. But even if it had been a whole army, they would at least need some method of mass heating to melt the ice to move more freely. If they'd elected to have Y'shtola use her wonderful Archon brain to freeze the water, she wouldn't even have to freeze it all. She'd just have to freeze a small amount, enough to make running over it or leaping over it a non-option for the pursuers. Just enough to get a lead on running away, which we already had.

As for ranged weapons, in this scenario, that single bow woman(almost all Braves/Blades used swords) never even catches up to be within arrow range, and on top of that, the only reason Thancred got hit was because he was already blocking the strikes of two people he was fighting.

Lastly, players in DND are notorious for not thinking things through, and DMs can be douchebags. Other times, not so. That's irrelevant to this hypothetical though, because neither of us are the DM or the writers for FFXIV. I'm just tired of people crediting Y'shtola with good thinking, when it was anything but.