> Congress as an institution has low approval rates because people dislike what it does in aggregate, not what the people they have a vote in doIn other words, people like their individual representatives because those representatives favor their preferred policies; but they strongly disapprove of Congress as a whole because they don't see any of those preferred policies actually being enacted.
> If Congress was more effectively representative—which is a matter of apportionment and electoral system—the aggregate approval would be higher.
This assumes that, by changing apportionment and the electoral system, more people would see Congress enacting their preferred policies. I don't think this is true. I think the reason Congress as a whole doesn't enact anyone's preferred policies is that there is no broad bipartisan consensus behind any of them; if a majority exists at all in favor of any particular policies, it is a thin majority, and there is no majority with enough consensus on a range of policies to be able to make the required legislative deals to get those policies enacted.
In other words, Congress is reflecting the fact that the country as a whole does not have a broad consensus in favor of most policies that are on the table. And in that situation, those policies shouldn't be enacted. So I would argue that in this respect our current system is doing exactly the job the Founders intended it to do: it is preventing thin majorities from imposing their preferred policies on everyone.
However, the disconnect between individual approval ratings and the overall approval rating of Congress does allow something else to happen: since there is effectively no competition for individual seats, there is no accountability for bad policy decisions that do have broad bipartisan consensus behind them. So those decisions can be, and are, made with impunity. The grant of power to the FDA that I mentioned previously is an example: there is no serious opposition from either party in Congress to granting unelected bureaucrats in Federal agencies extremely broad powers that affect everyone and cannot be effectively challenged. So that disastrous policy decision continues on while people squabble over policies that have only thin majorities, if any, in favor of them.