You just described how it is a systemic issue. It’s not a case of bad apples but the system itself.
Your true hypothetical is even more damning.
(Yes, I know about Citizens United - it has to be repealed, which is of course possible).
I can’t tell what you would consider an improvement, that number being higher or lower?
The 3.5 billion doesn't go to congress people. It goes into reelection coffers. Or as the sibling points out into electing-others-coffers.
We like to believe in free-and-fair elections, but in most cases the options are "unknown names". Most people vote party, not person.
The real "electing" happens at the primary level even all candidates are the same party. At this level money talks (through advertising.) Basically its a most-money-wins setup.
Congress is the pinicle of the iceberg you can see, but the real action happens at state level, in primaries, etc. That's why you end up with "2 bad choices" come election time.
The only way to remove money from politics is to ban TV and internet political advertising. (And it won't shock you to discover TV and internet think that's a bad idea.) Frankly, I'm not even sure that would help.
Politics bows to moneyed interests because politics is built on access to advertising money. RFK didn't drop out because he lost interest, he dropped out cause he ran out of money. He then sold his endorsement to the highest bidder.
Ultimately US society values money above all else. So it's not surprising that money is at the root of US politics. As far as the system is concerned this is not a bug, it's the killer feature.
The reason it seems like congress is so beholden to corporate lobbyists is because corporations are the only ones who take lobbying seriously these days. Grassroots lobbying being taken seriously is what lead to the passage of the Civil Rights and Clean Air acts. Even today, there are examples of grassroots lobbying that prevails over corporate interests. A handful of nimby can perpetually stall billions of dollars of real estate development, and there is no way billionaires like Peter Thiel are happy that abortion bans have cost the Republican Party so much political capital.
[1] https://slatestarcodex.com/2019/09/18/too-much-dark-money-in...