Governors DO make more effective Presidents. Reagan, Clinton, FDR...arguably three of the most effective (not necessarily GOOD) guys in office—the executive experience of running a state translates well into the executive federal branch.
Legislators are more on the outside of the executive arena.
They don’t, USUALLY make effective Presidents.
One exception: the unsung President Polk, who was ONCE Speaker of the House (the only former SoH to become President, by the way)....
But generally speaking, men who have only been legislators are not very strong Presidents.
Of course, perhaps in this day, we do not want a strong executive branch.
I taught Jr High American history for many years and am always amazed at how Polk is so overlooked. He added Texas, Oregon Country, and the Mexican Cession to the U.S. fulfilling the idea of our nation stretching from sea to sea. And he did it in one term.