Isn't that actually a major cause of the trouble? You expect Congress to deal with more and more complexities but limit the number of people (i.e. experts) who are members of it, causing them all to be generalists and moreover to have to spend more of their time campaigning rather than debating because the value of each seat is higher and correspondingly so is the effort someone will put in to take it from you and the proportion of your time you have to spend merely defending it.

Meanwhile people feel that their vote doesn't matter because a member of Congress now represents almost a million people and then ordinary people can neither affect the campaign nor get the ear of their own representative.

Suppose it actually had ten thousand members. Then they would be ordinary people. The members who are doctors would understand both medicine and medical bureaucracy. The members who are engineers would understand technology. Instead of them being lawyers whose first job is campaigning.