The Senate is one of the only things keeping the country from becoming a tyranny of the top N biggest cities over everyone else. We need it, or something like it. People in coastal cities openly hate the rest of the country, derisively referring to it as "flyover country"; there is zero chance that people in such states would have their needs met in the slightest under your system.

The real biggest problem in the US is the steady power grabs by the federal government (most notably by FDR but he wasn't the first and certainly wasn't the last). The federal government has far too much power, completely illegally under the Constitution, and it causes most of the acrimony in US politics. You simply cannot have one central body adequately meet the needs of both NYC and rural Wyoming, but we are determined as a society to keep jamming that square peg into the round hole. We desperately need to dismantle power from the federal government and return it to the states, who should've held it all along.