You’re only looking at one side. Regulations can also encourage corruption - if I can’t even open my doors unless I get a permit, well, that’s plenty of incentive for whoever control that permit to ask for something to “sweeten the pie”.
On the other hand, campaign contributions are common, legal, and involve large sums of money (especially to PACs).
Systemic corruption of elected officials, resulting in de-regulation in order to benefit wealthy shareholders at the expense of the public, is more concerning to me than the possibility of low-level officials seeking bribes.
To me, someone funding raising through a legal, transparent PAC might not be desirable, but it’s far less insidious than backroom dealings that pervert the rule of law.
It seems strange not to take the next logical step and conclude that there were some backroom dealings, especially if the politician later takes an action that is favorable to the donor.