
Originally Posted by
Lauront
A big part of it is the fact that the sound preceding the monsters manifesting. That subverted their control over their ability to manifest creations. So it's quite reasonable to think that, besides the onset of panic, they were cautioned against directly engaging these beasts, lest they get hit by the phenomenon and add yet more monstrosities. They had devised so-called "guardian forces" - primals by all accounts - to combat it, probably because they're not susceptible to this sound. These monsters were different to beasties which might be trivial to defeat to them, because those can't put their own powers to work against them. They were in essence fighting the products of their own power because of how the Final Days operated, hence why it was so insidious. If we take the ancient shades that Emet summons as representative of the ancients, they could at the very least wield some potent elemental magicks, but the bigger issue was how the phenomenon spread.
My guess is that the Convocation will have had combat specialists in it. At the very least there was Azem but I'm going to speculate some of the others were as well, because they cleared the path to summon Zodiark, and we've seen at least Emet (sorcerer of eld) and Gaia (yes, sundered, but able through Eden to seemingly recreate her ancient self) take on higher forms, as well as references to Lahabrea's brilliant fire creations - bearing in mind the Lahabrea we saw was a shade of his original self. As time went on they probably refined their innate talent in manipulating aether to the more potent forms of spells fuelled by darkness that we now see them use.
Rushing in to kill re-creations of the beasts, that wouldn't spread in the same way when encountering the MC and their party's sundered life forms, isn't quite the same thing.