In that fight, Supes did use heat vision. Slade parried it with his Promethean Blade, absorbed the energy and hit Superman with it.
Freeze breath conspicuous by it's absence.
In their second fight, Slade is actually smack talking by being like "Hey, Superman! You could totally get by my shield if you chucked me into orbit or burned my face off and shit but you won't do that because you don't kill haha,"
So, by and large, they are at least acknowledging that Slade is exploiting CIS rather than implying that he's actually legitimately throwing hands with Supes. Which is a step forward methinks.