Byakko was the last time I bothered farming an Ex Trial. The difficulty of Extreme Trials pretty much bottomed out with Sophia Extreme in 3.4, and they never really tried making them more difficult than that ever again (Shinryu being the one exception), where Extreme Trials were originally about as difficult as third floor (fourth floor in original Coils) raids. I suppose if I had started the game with the newer ones or wasn't mostly engaged by fights being challenging or having unique mechanics (mechanics that aren't just different versions of "dodge here and there"), I might feel differently, but I was already used to the style of extremes they had before they settled on the newer approach.

It's also why I think they skipped Nidhogg, Ramuh and Moggle Mog; those fights would be way too difficult simply because their design paradigms have downright alien ideas to the vast majority of trials in the game. Targets you shouldn't attack? Baiting attacks?? Buff management??? Not to mention King Mog draining MP from DRK or PLD today would be unfair for job balance. They probably skipped Bismark because that one was a bit dull (in terms of pure difficulty, maybe still a tougher fight than some modern extremes just because of dps checks and jobs were suddenly harder to play in HW), and Ravana of his counter, mini-dps checks with the Warlord Shell and the stances that reduced / increased his damage taken would mess with their 2-min meta.

Byakko, and the two other four lords, in particular suffered from having an 'interphase' that was basically identical to normal mode, and wasn't really designed for being a fun, repeatable part of a fight but rather a novelty the first time you see it.

First time running Jade Stoa, riding a tornado up into the air and playing bullet hell was mad cool! "Oh boy, I bet this'll be CRAZY on extreme!" I thought. And then... it's almost exactly the same. You can dodge everything in that phase moving less than the size of a Ley Lines, during which the only thing you can do is move, and it's a whole extra 2 minutes of the fight.