I agree with the point that populists have a strong incentive to not solve problems, but I'm not sure that means populists can't be effective. For example in US history FDR was arguably a populist, and I would say pretty effective. And while the US populist party imploded fairly quickly, a good chunk of it's policy wants wound up happening in the next decade or two during the progressive movement.[1]

Using the power definition of politics, it still seems to me that because the ability to exert power is only given when there is a need to be solved, a (for example) plutocrat has a similar incentive not to solve problems as a populist, and would be similarly likely to not be effective. I suppose an explanation that's consistent with both perspectives is that political leaders in general are not effective.

[1] https://historymatters.gmu.edu/d/5361/