Exceed isn't useful
Hold your horses.

[Event 70] Raid Event vs Iwanaga-Hime-amonglare.png

You do realise it's not just burst cap up but also burst dmg up right? Assault S exceed S is infinitely better than assault M.

Burst cap
No matter which buff, all single bursts are absolutely capped at 2m dmg, after which the 90% dmg nerf applies. The only known hime to ignore this cap so far is Meta AW, when she bursts at 0 countdown.