Uh, if the Senate has less power, then each state does not have its equal representation in the Senate.
The Constitution does not require all States to approve all changes to the Senate. Only those changes that would cause one State to have more Senators than another. If it did so require, then Amendment XVII would have needed all forty-eight States (now fifty States) to have approved it instead of just the thirty-seven that did so. So long as all States have the same number of Senators, there is no violation of the equal representation clause no matter how little or how much power is given to the Senate.