The prime example was 2016 where the spending was more than 2 to 1 in favor of Dems. And they also secured 57 major newspaper endorsements compared to just 2 from the other side. They just threw money at it. Same thing happened in 2024 presidential. And recently in NYC mayoral race, it was even more lopsided with the person who spent less money blowing out the one who spent more.
The more likely impact of money is being able to get your message across at all. There's a saturation point. In any of these, does anyone think that if losing side spent twice as much money on their messaging they would have won? I don't. The only thing that might move the needle is if the little guy wasn't able to spend what little they spent to bootstrap support.
Of course you can try to do so without spending, like walking door to door, but that doesn't scale very well. So I think restrictions on paid political speech will help incumbents.