I have tested the damg with of Tobi with different classes and found out that when Tobi is with the Fire main his chase does a massive damg even when he hadn't got any damg buff. I play Water main and my Tobi does only 1k -1.1k damg but my friend play Fire main and his Tobi does ~2k damg. After I defeated his Fire main, his Tobi chase return to 1k - 1.1k the same to mine. We did it several times and the result is the same.
Please take a look at this bugs , it makes Fire main too OP compare to other mains.