It’s true that Congress often has its own agendas and interests. However, its also true that Congress has become far more ideological and partisan than ever in the past.
Both parties used to have a spectrum of members from conservative to liberal. The “solid south” that the Democrats controlled from after the Civil War until the Civil Rights Act was extremely conservative in the terms of the day, and a Democratic president could often expect opposition from them.
Rockefeller Republicans represented the liberal wing of the Republican party. They were mostly from the northeast and were bitter foes with the conservative wing once represented by Taft and McCarthy, neither of whom got along well with one another either.
Changing demographics have mostly obliterated these ends of the parties. The Democrats lost the south to the Republicans. Although a few house candidates have won because they presented themselves as conservative Democrats, virtually the entire Congressional slate is moderate to liberal.
And the Republicans have been wiped out in the northeast, There is not a single Republican representative in the New England states or in New York east of the Hudson River. The entirety of Congressional Republicans are moderate to conservative.
Without the need to placate one wing of the party, any president today can expect almost full support from his party and almost full opposition from the other on every important issue. It’s always been good for a president to have his party in control of Congress. These days it’s utterly crucial. The world has changed and the parties are more divisive but less diverse than I’ve ever seen them.