Notice, that they approved it. And it was already done, by the President. First by his council, then by his Executive Order. The House and Senate had an interest because the new EPA would be taking responsibility of a great many programs that were being controlled by the Departments of Interior and Agriculture (specifically dealing with waterways). The President can make a new department, but not simply remove powers from one and give them to another. That takes Congress.
You present a simple "Cliff's Notes" version, as if that proves your point?
Congress did not create the EPA. It already existed, and had since 9 July 1970 when President Nixon ordered it into being. What you are talking about here is the hearings that lasted into September that gave the final approval, closed some departments (like the Environmental Health Division of the PHS), and turning over their job to the new EPA.
By 1970, it was clear that the nation's approach to environmental problems wasn't working
time.com
Now as typical, the President can do a lot of things, but needs Congressional Approval for them also. That is why a treaty is not really a treaty until ratifies by the Senate. And he can appoint judges, but they need to be ratified or they are only judged for a set term. A President can create a new department, but needs Congress to allocate it a budget and give it the power under law to enforce things. This is what you are missing. You are confusing that part with the creation itself.