So I've been told my reading skills are lacking, and they may well be, because now that I've re-read Leading Strike, it appears that feat not only has no limit on the number of marks you can stack in a single round, it's also worded as if merely attacking (and not actually hitting) triggered the extra damage. The last part is probably just my early onset dementia talking, but even if it requires a hit, it still seems kinda good, especially if you have reliable means of triggering a bunch of AOOs between your frontliners.
Fuck, I didn't expect to be so invested in munchkining this game. I certainly didn't feel like doing that in Kingmaker.