Why would you put Law in a battle against Nami in the first position? He'd have more chance of defeating Chopper, Sanji or Franky. The fact is, without his Devil Fruit, he hasn't shown any sort of superhuman speed or strength. We know he was trained by Lao G in martial arts, and, swordmanship by Diamante and Gladius taught him sharpshooting. Without those aspects, nami would have plenty of time to prepare herself.
With Mirage, Law would be oblivious to what is going on. If you can't see your opponent, you can't hit your opponent. I can see Nami losing to Law's CoO, though, though he hasn't used that part all that much. If he can find Nami past her mirages, then maybe he'd have a chance of tanking her attacks, but I doubt it. Nami's lightnign has become very powerful, and she is resourcful enough to catch you in Lightning traps with great ease. And her wind attacks already showed great ofensive capabilities, I would expect she'd be able to get Wind as a defense as well. So, even if Law can sense her, I doubt he can get to her, being pushed back several times. And even if he can tank more than one Lightning attack, if he can't get closer, he can't do much. Then again, if Law were to use a gun, Nami migth be done for it.
That's the thing about Usopp as well. He's very resourceful. Without his DF, Law doesn't have any counters for special attacks. His martial arts are very good, but if your opponent prevents you from reaching him, what will you do? Again, Law hasn't show any speed-attacks with the exception of his Ope Ope teleportation. And, with Usopp, a gun isn't as efficient, because he can counter it shot for shot. If Law passes Nami, he wouldn't be able to pass Usopp. In the odd chance that his endurance allows him to surpass Usopp's cleverness, same as Luffy in the Water 7 arc, then he'd be stopped by Robin.
No endurance can tank a cracked spine. Oars is the proof. I passed Chopper because chopper is a physical fighter without much martial artmanship. he has a Kung Fu point, but Law was trained in martial arts his whole life, even if he forgot most of it after getting Ope Ope.
Those are my reasons.