There are two interlocked selection mechanisms: politicians select the issues they pursue, and sponsors select the politicians whom they want to give voice (and money).

In dumb evolutionary environments and in anthropics, there is no direct feedback between these two mechanisms. Bacteria get born, behave in a predefined way, and either procreate or die. Successful bacteria are not smart, but simply lucky. They are selected for fitness by a dumb process.

Similarly, activists enter politics to pursue certain interests, these interests do not change significantly, and then the newcomer either gathers enough support to get elected and influence public opinion, or doesn't. Sponsors select the politicians which have already taken a favorable stance, and help them get heard and get elected. Successful activists are those which pursue important issues which attract support and sponsorship.

I suspect that this is how the system is supposed to work, but it breaks when politicians can be adjusted, that is, bought.

It's not that money gives lobbyists's words extra weight. Money allows their words to be heard. That is, without the contributions, you don't get to talk to the politician. Contributions are an entry fee to a meeting.