Why the US Marine Corps paired a few heavy tanks with lighter forces

Did US Marine Corps doctrine explain the continued development of the M103 heavy tank?

Yes. A limited heavy-tank component was intended to support a main tank force that remained as light as possible.

An amphibious doctrine's formal ambitions still depend on the vehicles that ships and landing craft can move. The US Marine Corps interest in a limited number of M103 heavy tanks concentrated heavy firepower while keeping its main tank force lighter. That balance depended on lighter vehicles travelling with the first assault wave. Once the nominally lighter tanks approached the weight of the heavy ones, they could no longer accompany that wave, and maintaining both types became harder to afford.