Also for being such a "shooter" his 3 point numbers his first 4 seasons in league have not been that much better than what Nance has been doing the last 3 seasons (LM 36% for career, LN 35% last 3 seasons).
I don't think you judge Markkanen as a shooter just by his percentages. When you watch him you can see he has some special qualities that separate him from other big man shooters.
Namely his ability to get his shot off quickly, off of movement, without much space and with extra distance.
So I am talking here about pick and pop big man action. Some bigs can only shoot long shots when their feet are set. Other bigs can shoot off of movement. These bigs are more of a threat on PnP actions because they can create a higher number of scoring opportunities for themselves than bigs who struggle with their feet. This increases volume in terms of how many 3s Markkanen can create for himself.
You also see Markkanen with his speed, agility and ability to catch and shoot off of movement in situations where there is movement leading to cuts / darting out to the three point line (like guards do) rather than a strictly stand still shooter (like Brook Lopez). Again, this creates volume. More volume for Markkanen vs stand still shooters like Brook Lopez or Myles Turner. It also creates more off-ball movement in your offense making your whole team offense more dynamic & more difficult to defend.
The amount of space a shooter needs to get off a shot is an important quality that again leads to higher volume. Think of Al Horford who needs a lot of time and space before he is willing to shoot a 3. This makes him a reluctant shooter who shoots only low volume of 3s even when he is shooting well.
And then the range, Markkanen cannot not just shoot 3s but he can step a few feet back from the three point line and still be a threat to score. This stretches the defense further improving spacing for his teammates. Forcing opponents to defend him tighter and further from the rim. Gravity.
All in all ...
This makes Markkanen one of if not the most special 3 point shooting big man in the league today. It is the variety of shooting opportunities he is able to create for himself which leads to much higher volume than most 3 point shooting bigs can manage.
So say he is shooting 36% on 8 threes a game vs another big who is shooting 36% but on only 3 threes a game (Jokic's volume). Who is more of a threat? Who is the defense more scared of shooting the ball?
Markkanen has not gone up to 8 threes a game yet but he can if his team actually makes him integral to their offense instead of using him off the ball in the corner like the Bulls often did (which is why he is around 6 threes per game today).
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Going back to my initial point about judging shooters solely by percentages. I think we need to couple percentages with volume somehow to come up with a better number for evaluating shooters. Volume is under-valued in terms of three point shooters.
There is a lot in volume that explains a shooter's value that is not fully explained by percentages. Same with volume not fully explaining value without percentages (Antoine Walker). We need to couple them together somehow.