In contested elections both sides usually have a large amount of spending. If you only read the headlines you’d think it was only the winning side that spent any money.
Another thing that isn’t obvious is that PACs have high win rates because they’re usually strategic about which races they go after. The money influence can only move the needle a little bit, so they need to pick races and topics where the voters are already close to evenly split.
There have also been a lot of high profile examples of extreme spending on elections that didn’t lead to the desired outcome.