They don't give you millions of actual money that you can spend. They help you win (or try to stop you from winning). It's taken by some to be self-evident that the political system is corrupt or that campaign donations influence policy, but the narrative unravels if you look for evidence or thinking more deeply about it. I think if we're looking at why some unpopular policy passes, right-wing identity politics is a bigger culprit than the corruption theory.
Look at the group. How many people at least imply that they want more pro-worker policy, or even UHC, but that the real threat to America is college students being overzealous culture warriors or television commercials showing too many interracial couples? Or in the last presidential election, there was a dispute about whether Clinton or Trump was the more "pro-establishment" candidate. Clinton was widely respected, highly educated, and experienced so some saw that as making her more "establishment" than Trump, who "respectable" people considered to be a buffoonish crook. But on the other hand, Clinton's policies were far more pro-worker and pro-consumer while Trump's were more pro-owner and pro-corporate. So people got back at "the establishment" by ... giving them everything they wanted and more and fucking themselves over. That dynamic, rather than campaign finance, is the issue.
Again, change is designed to be hard to come by because publics tend to be overeager to make drastic and stupid changes. In our case, there is massive disagreement about the kind of change needed so no one wins by a big enough margin to get their wishlist through. That's frustrating for everyone at times but also good for everyone at times. Overall, though, living standards have been rising for all classes of Americans for 100 years--we've gotten richer, healthier, more free, more-entertained almost nonstop in that period. Crime is on an almost-30-year decline.
I think if you consider compromise to be corruption, it can be seen as corrupting by its nature.
I think it's more about getting more money to help right-wing politicians win. It's not a huge issue at the level of national elections, though.