I could not disagree more. Policy should be directed by the Executive Branch - not the Legislative Branch. Legislators know nothing about management and leadership. (See: Barack Obama). Presidents have no counterparts in the House and Senate. Legislators can always abstain from action. They can always have a do-over if their actions come under fire. Presidents do not have that luxury.
I think you misunderstand. Yes the president comes in with an agenda, and what we’ve seen with Reagans and such is that he’s got key people in the senate and house they work with to create legislation and get it through both chambers. Not necessarily already having the entire thing written and then just saying ‘pass this’. The executive doesn’t get to be the legislative branch. They have to work together. It also gets the needed ‘buy in’ from key people in the legislature to push for it for the president.