Lu Bu would be so broken with armor and damage lol. The ones that'd scare me would be Nemea, Hundun, and Xu Shu. Resets for daaaaaaays.
Heck the amount of amazing tier characters Koei has in their Warriors games to put in a vs fighter is mind boggling. Top ones I can think of.
- Jia Chong- thrown axes could be far scarier than Ouroboros IMO
- Zhao Yun-Pressure character with the range of a spear...Vergil 2.0
- Fa Zheng- he throws a magic carpet out for his attacks and has stun states. Basically HUGE hitbox traps and insane meter build with stuns. Guy would be crazy for damage and finishing big.
- Kunoichi-Wolverine meets ...every thing lol.
- Yoshitsune Minamoto- laser sword that gets bigger and does more damage every time he lands a command grab that dashes forward? Plus he has Zero's buster. Oh hell yes, why isn't he already a character?
- Nezha- placing large multihit waves of energy on the screen that draw folks in while possessing the highest speed and dash range plus thrown ring weapons and multiple launchers. All around crazy fun.