Would making Blastoise Water/Steel help or hinder it? Would you use it if it was a Dual type?

I just had a look see over both Blastoise and Empoleon and I feel like Blastoise deserves the Dual typing when it goes Mega He can learn more steal type moves than Empoleon too even if its just one.

Whats the point in looking like a Defensive god if you cant really be one?