Yammato erased the ground beneath him while orochi only melt the ground.
Yammato still passively Vapes.
The ground near Yamma was still mostly intact. Orochi's fire cannon is more impressive. Bearing in mind that Saitama has gone completely unharmed by every heat attack he's ever been hit by, Genos, Orochi, etc (his only concern has been for his clothes).
Also, as I've said far too often, blut vene was able to tank Yamma's passive heat, and if you want to argue a normal Sternritter's blut vene > Saitama's durability then kindly don't reply to me.
And I have already made a case for why there's a good chance Saitama won't allow Yamma to land a hit on him after he sees all those flames.