I don't, but it's mostly because Shiro probably isn't willing to go all out on Sapphire. When it comes to speed Shiro matches Sapphire, and he's not exactly lacking in the damage or durability department. If he could muster the imagination to do so, he could also twist his Illusion powers to be more effective than Sapphire's own disappearance based Semblance. But what he lacks right now is the will to harm Sapphire, which is why he's most likely going to lose. He needs to be more vicious.
I wouldn't say match her speed, if he dropped his sword and shield to go claw to fist maybe. As far as his Semblance he won't be receiving his full illusionary powers until he receives enough credits. Even then those may go to a bunch of minor weapon and ability upgrades if not an entire subplot.
Remember I altered and rebalanced his Semblance for this world because I felt his original semblance to be too powerful.
And you're right, if Shiro and Sapphire do throw down she would win because he doesn't have her cold heart. If she decides to anger the tiger boy and push the wrong buttons then that may go out the window. He'll want blood then. She Just has to know what to do or say to flick his switch.
