Surely, Kal's advantages would be much watered-down on Mars as opposed to Earth where he'd clearly be superior.
Whoa. What an interesting idea. Jor-El deliberately choosing Earth over Mars precisely because he wanted Kal-El to be the physical superior of those around him.
But on Mars, Kal-El would have been more at home, I think. He would have been raised by people with powers much like his own. He might have even learned more powers than he could on Earth.
I'm glad you liked that idea, Daybreaker.
One also has to factor in that Earth is a lot more like Krypton's environment than Mars is. Jor-El was already settling by giving up on a similarly advanced world, so he wasn't going to give in even more on the ecology if he could help it. His primary consideration was giving Kal-El a home as safe and similar to Krypton's as possible. Mars is a barren wasteland compared with Earth for ecosystem.