If two politicians are equal in every other respect but one was better at basketball… I guess go with that one? I mean, all else equal they’re maybe a better team player or something. But that line of thinking doesn’t mean we should only ever vote for ex-NBA stars.
There are plenty of similar potentially attractive signals: veteran status, success in business and/or being a fake billionaire, academic success, acting, etc. Some signals are stronger, and some imply a smaller pool of candidates. If there are more successful business people in the world we should expect to observe more of them transitioning to politics than, say, world-class bowlers. Likewise, if the signal is more relevant (e.g. law degree vs. paleontology degree), it makes sense to see more of them in the wild.
That 18% of German politicians have PhD’s seems wild to me. Maybe I’m biased because I work in an organization full to the brim with PhD’s. But that many politicians with degrees seems about as reasonable and as likely as having half of Congress be elite athletes.