Pet PDT and MDT both cap 87.5%
It has been like this since SE nerfed it in Abyssea days. before that there was no cap (but cap was unreachable until abyssea). so a few of us unscrupulous players were abusing the crap out of completely invulnerable pets in abyssea.
just playing the game how they programmed it...
Ironically they nerfed smn... and didn't realize for another 6~8 months that the same mechanics applied to pup and bst.
Pet used for burning Yakshi is BouncingBertha/ScissorlegXegin.
I like to throw Killer instinct up for defensive purposes during the zerg.
Temp Item: Mirror tonic > Fight > Run Wild > Spur > Unleash > Tegmina > Fight > Tegmina repeat for 30s and hope you doing enough damage to bring it down.
I've seen groups fail because they refused to account for HP growth and tried getting 3/4 bsts to take yakshi down w/ 8 ppl in alliance.
You do not need to have Aymur to burn down yakshi. if you have 2x smn, you can alternate mewling and completely prevent tp moves. This makes the fight much more manageable and you don't need to use Sp abilities.
I really don't know about BST, BST, SMN. BST, SMN, GEO seems more likely to succeed. but I would not AC mewling. I would just AC the most damage you can. having the cor pet rolls and geo frailty bubbles means bst pets have capped attack. I don't know smn well enough to understand the exact mechanics in a good AC zerg. but I think the damage would be good.
I think that often means about 34k damage per Tegmina.
I haven't tried using Falcorr in unleash zerg against Yakshi.. but if you can cap attack w/ falcorr (which you can do vs Maju w/ cor and geo) Then you can drop 50k~80k back heels at a slightly slower pace than you can spam tegmina, but potentially more/faster damage.
I was in a pet party that did that vs maju. pup tank (me) bst and smn dd (used AC and unleash starting at 50% hp) rdm to blind. geo and cor to buff.
I would suggest the bst, smn, geo with cor dropping would probably work pretty well. if he's still alive when unleash and AC run out, I suggest mewling spam and turtling up the grasshopper until you can widdle away the last few %.
A balanced and buffed pet party can handle most any content.
this would be:
geo
cor
pup
bst
smn
and have 2x of one of those jobs or bring something in that complements. a RNG, blm, rdm, or sch works well also. Its incredibly powerful.