A small town mayor has none of the power a member of congress would.
In democracy the larger the seat, the larger the infrastructure required to get there.
The funding of this infrastructure brings the necessity of corruption.
Assuming the mayor is in an executive mayor system (not a council-manager) system, they often have far more practical power than a member of Congress over any issue, but their power is over smaller issues. Even in a council-manager system, the mayor (who is a primus inter pares council member) is more likely than member of Congress to have decisive power over any issue within their ambit.
(Also, being a small town mayor, or similar local officer, is not an uncommon way to build the infrastructure for becoming, say a state legislator. And that's a way to build the infrastructure for Congress, and that for Senate/Governorship, and that for the Presidency.)
The government, for the most part, is not an evil cabal of deep state cultists (in most countries that describe themselves as liberal today). People like you or me can join a party, and then get elected within a year or two.
What I absolutely do believe is that people elected, through what is essentially a harmless popularity contest in peace time, are the worst type of people you want to have taking decisions in a crisis. People worried about their next re-election are _not_ going to make the right decisions, apart from the fact that in peace time the electorate optimizes for populism and extremism, and the candidates are sometimes more like actors than leaders. In short: they are incompetent, heavy handed and not even remotely equipped to deal withe massive leverage attached to the levers they control.