Exactly. Its not a fair comparison at all. The bigger the sample size the more probability of regression to the mean. All those players who are above Ronaldo on that list and have taken significantly less penalties, will have their success rate lower for sure if they took 100+.
30-40 penalties is plenty big enough of a sample size. That's 3-6 seasons worth of penalties for most regular penalty takers. You get a pretty decent picture on a players ability to convert them during such a long period.
You can of course also always reduce the size of Ronaldo's sample to that ≈40 penalty mark. For example we could only look at his time at Juventus and his conversion rate would still be around 85% with around 40 penalties taken.
The assumption that for some reason the conversion rate of players like Lewa and co suddenly just nosedives is based on absolutely nothing. They've taken penalties already for years consistently converting them at those rates. Of course it's possible that for some players it would come down just like it's possible that it goes up for some players.
- - - Updated - - -
Not the same thing though. We have a controlled situation with penalties i.e. everyone kicks from exactly the same spot without any interference from the defence. In basketball the position of the shot and the defenders greatly affect the difficulty of the shot.