APBRmetrics

"All are strongest thru 8 or 9 , with really weak contributions in the 8-9 spots."

And the 13th or 15th man?

I found your quoted line in the opening post:

So here is an example resulting in the correlation line for Miami in their one series vs Boston. Butler and Rozier weren't playing, and their coach had to improvise.
The player stats were recorded after the 1st round, 2nd round, etc.
All 4 stat correlations are weakest at 1-7, where #7 Delon Wright looks like one of their best players.
All are strongest thru 8 or 9 , with really weak contributions in the 8-9 spots.

They only used 12 players.

Used 12, so 13-15-18 not important, not helpful in the playoffs. As expected, in line with their relative performance in regular season. Negative impact likely if they had been used, so they weren't.

Missing both Butler and Rozier, they were already digging deeper than preferred.
Teams stick with their better available players in postseason. But 2-4 of top 9 showed up as sub-zero.

In any use of the words average or below average, one should clarify mean or median. Mean is higher than many realize. Median is something of an achievement. Often paid well... but if you can buy near median performance for less or way less, you get good value... as an employer.

How would one define median scoring rate, rebounding, or win production? Include players with very few minutes?
Average and mean are synonyms, but mean can mean a lot of things; even mean people know that.

Include or not include what you want. Mean what you want to mean.

One persistent phenomenon that seems to suppress correlations between minutes and these stats: Separated by positions, SF and SG get the most minutes and are the least productive (or proficient).
Showing fraction of total minutes, and of 'wins' contributed: This is last season's distribution, using b-r.com's position designations.
BPM I believe has a distinct position system defined by stats, and it measures players differently based on those positions.

Where the % of wins is more than the % of minutes, that position is seen as generating more than average wins per minute.
BPM diminishes the value of Centers, relative to the other 3; and Guards get relatively more credit.
Possibly a clearer form -- just dividing the %wins by the %minutes: 1.00 is average. There's a factor of 2 between some positions. SF get no respect!
I propose that the seeming contradiction is that PG and C are often not suited to slide to the adjacent position. Small guys tend to have defensive limitations that put them on the bench. Big guys are less suited to sprinting against small-ball lineups.
Playing 3 or 4 shooting wings may give a team an advantage; but those guys are sharing X number of shots, while a big collects plenty of rebounds, putbacks, alley-oops.

In a boxscore system, boxscore production is measured. Rebounds and assists substantial differentiate. Being the lead ballhandler / passer and the generally closest to the basket / biggest rebounder and often rim defender matters generally. Dexterity and speed / agility don't necessary have a size but size & strength does. Coaching and experience pulls many players to one pole or the other.

Wings remain largely because of scarcity of those talents and lead positions and maychup defense.

You probably need some wings for defensive matchups with some other wings. But how many? How often can you play extra "PGs" and "Centers", guys most advantaged with their physical advantages and learned skills? How many can adequately cover wings?

There has been occasional use of 2 PGs and twin towers and studies of those cases. I have done some small studies and reviews of such work but don't remember the findings in detail. Review and new work may help.

There are limits on time handling the ball
/ directly the offense and for rebounding and protecting rim, so duplication may see diminished returns but perhaps more returns than using wings at least in those categories.

Average impact by position using metrics with RAPM should come into this conversation. I basically recall PGs and / or especially Centers dominating here too but would want to re-confirm. It would make sense that playing larger than average roles on very important tasks would see that evidenced in RAPM ratings.
If anyone wants to dig up the best resources for that or do a new study, great.

Big PGs who can handle switches are of interest naturally, as are bigs who can participate in moving the ball with hands, feet and judgment.

Many still lust for wings, especially those who can do more than average on PG skills and big skills. And / or 3pt shooting and defense and switch based defense. That is reasonable. But apparently dual small / big skills above average are pretty rare.

Player acquisition should be driven by skill acquisition but sufficiently spread to all skills and cognizant of them in lineups and in proportion to importance. As measured by metrics or basketball eye & mind based. Winning based is best.