If Nylander or Marner had the shot and finish of Boeser, they may have 25 goals each now. But neither do, thus some players sport higher shooting %'s. Something that is often never cited when the shooting % argument is brought up. Thinking or arguing all players have the same quality of shooting ability to blindly cite shooting % is one of the dumbest things I continually read on these forums.
You touch on a point then speak in hyperboles to make it. If Marner and Nylander start hovering closer to even league average, they'd score a lot more goals just by sheer volume. Marner, while very much, a primary and secondary playmaker is shooting ~5%. And agreed, Boeser is a incredible finisher and I've said as such, but right now, he's pacing above any single of Stamkos's years in terms of SH%, including his 60 goal marker (at 21.1% right now). And I used that comparison because Stamkos is the general outlier when it comes to SH%, having a career SH% of 16.9% and the pedigree to back it up.
Basically, the numbers that Boeser are posting, so far are historical numbers. And again, while I don't deny he will always be above the general league average in terms of SH%, there is no precedent for it. It's almost like Stephen Curry with his 3 point numbers, not only in regards to efficiency but volume. It's precedent setting stuff, except in this case there's no framework to work on.