He's just deliberately not getting it at this point. I grant it is not a simple concept and the single tweet that he refuses to read most of obfuscates some of what's trying to be expressed.
I'll try one more time, even though this is getting into one-armed drummer territory.
Forget Nico Hischier. Imagine a Player X. What if we looked at every shot taken on the power play in the league, taking into account the pre-shot movement and location of every shot, and came up with a metric that determines, based on location and pre-shot movement, the likelihood of any given shot becoming a goal? Then if we take those numbers and applied them to all of the players in the league, we have Shooter Score, which we can then apply to any player, including Player X, not taking into account player X's boxcar numbers or perceived shooting skill. This is fundamentally similar to a concept like xG, but it is not xG. Goal results are only being considered here as an input, not as an output. That's why Nico has a high score - he took a good number of shots, almost all of them from close in, and by this metric and by others, probably should've had more PP goals. But maybe there's something fundamental to Nico or the power play why he doesn't - more investigation is needed.