That's how I used to think until I started actually meeting the "idiots." From up close:
1. The members themselves are usually ciphers and hood ornaments -- methods of collecting contributions and votes. There are a few truly decisive people: the president, a half dozen cabinet positions (although undersecretaries are usually the real leaders), a half dozen committee chairs. The other folks you see on CSPAN are fungibles.
2. The senior staff make all the work-a-day decisions and most of the important ones. When "vacancies" occur (the polite Beltway expression to describe death, retirement, or, worse, losing an election) senior staff with influence and experience land other jobs or join executive agencies, so the knowledge base stays intact. Senior staff are very, very smart -- top 1% in the top 1% of schools smart -- and very, very savvy -- shiv in your back if you mess with them savvy. They effectively are the government, affiliation matters less to them than contacts, and ideology is viewed as a game for keeping the rubes in line.
3. "Politicals," usually campaign staff or relatives of big donors, are given impressive titles with zero policymaking power. They disappear immediately after a vacancy because they never had any capital or knowledge to begin with.
Those are the rules of the game as it's really played, and they likely have been ever since direct election of Senators, if not before. The process makes the members look more idiotic than they really are, probably, but their distribution of intelligence is likely identical with their constituents.