Corny Company can back a candidate in the Primaries, sure. But if that candidate is a moron due to eating nothing but corn since age 0, tends to grope anyone of their preferred gender, and has zero experience in politics, they have to face the people twice: once in the Primary, and again in the General. Usually they will fail to get the nomination, and if the state is at all 'purple', fail to win the seat. In that latter case, it's such a disaster for the state party they will turn on Corny Company and take someone else's money instead. See, the candidates shouldn't (and usually don't) spend donation money on themselves and their family. They spend it on getting elected (as is legal) or re-donate it to their party (making their opinion more weighty within the party).
Primaries are one of the innovations I like best about the US. They're not even required by the Constitution: both parties developed the idea as "extra democracy". Either party now could make them more fair, by banning donations to primary campaigns and giving all contestants an equal fund, for their campaigns. As it is, serious offices like US House and the Senate are obtainable by candidates with no more than a term or two in a State legislature. But it should be even easier, talent alone should be sufficient. Another thing I like though, is that parties take members more seriously, allowing them to talk, when they demonstrate cross-party appeal by winning a difficult seat. The center is where the votes are.
While the idea of only small donations is good (the Bernie model) it's hard to stop employers handing out a "bonus" to employees and hinting what they should do with it. The US should definitely get rid of the SuperPacs, which I would do by ... uh, it's a tough one tbh. Citizens have the right to "petition for redress of grievances" and that definitely includes airing their grievances during an election campaign. Restraining political advertising ONLY to political parties, would be a partial solution, however before long there would be dozens of new "parties" and no legal way to stop them. It will sound crazy, but maybe give the top five parties ABSURDLY large amounts of taxpayer money, so they drown out the SuperPacs?
Government money is not taxpayer money, any more than the grocer's money is still your money as you walk away with bread and milk. Any time money is used, government is a player in the contract (as enforcer at least) so in a sense, it's their money even more than the grocer's money is theirs.