Without the filibuster there isn’t a dime’s worth of difference between the Senate and the House. Why do we need two Houses?
Excellent question although the filibusterer is not in the Constitution, it is the last remnant of what was the US Republic. With the Direct Election of Senators, the Chamber is like to house using the power of the federal government to bring home the bacon. Without term limits, they are entrenched power houses with ego to large to control.
We are no longer a Republic.
You have an excellent point. With direct election of senate and house and with no filibuster for the minority party in the Senate, we simply have a bifurcated unicameral legislative branch.