I've never used Edgar chains, but always hear about it, so wanted to try it out after reading your post. I cactuar'ed up a second Edgar (I'm overloaded with them, so didn't mind), geared a full team in wind weapons (including Gilgamesh in my best gear, 769 atk w/ Kazekiri wind katana) and went into the latest trial (March of the Beasts). Exact team was:
Gilgamesh (769 atk, wind weapon) -- Divider
Noctis (411 atk, wind weapon) -- Warp Break (on the tankiest target)
Edgar (wind weapon, full hp/def gear/materia otherwise) -- Chainsaw
Edgar (wind weapon, full hp/def gear/materia otherwise) -- Chainsaw
Refia (for Embolden)
friend Lightning (for Aero Blitz.... was the only friend option with wind)
Now, I'll absolutely say that team is far from fully optimal, but it was the best I could do since Edgars can't use any holy weapons (could have used multiple excalibur + an excalibur gilgamesh friend if they could). I also probably didn't have perfect timing, but I still chained decently enough.
First fight took two rounds to clear with the wind chains (1 mob died, the insect lived)
Second fight took two rounds (big ochu lived)
Third fight took 3 rounds (1 slime died first round, other two died second round, roper died after three rounds).
Fourth fight brought the flameblade mob to 60% life first round, then both edgars died to a single normal attack from the bosses.
Decided to give up the test at that point. I just don't see it. The only way I can imagine Edgars being viable in endgame content is if they're massively decked out in TM gear so they can live, and even then, the damage wasn't anything special.
Edgars were used for the Dark Ifrit trial? Is there a youtube video of that? I'm having a hard time believing it.