I think it's more precisely a 3-7-3 arrangement.
Assuming that "wings" are those who play the traditional SG, sF positions, why would one devote 53% of the roster (7/13) to "cover" 40% of the floor (2/5), while allocating only 23% of the roster (3/13) to "cover" the very important PF/C positions (also 40% of the floor), with the remaining 23% allocated to one position (20% of the floor)?
Even though SG and sF do share some characteristics, SG and PG do also (and those who are proficient at both guard spots are often called combo guards), just like sF and PF have some commonalities and certain players can do well at both. At the end of the day, the skill set that makes a player a great SG is similar but different to that that'd make him a great sF.
The most reasonable arrangement is to aim to having two players with skills appropriate for each traditional position, leaving 3 players to be allocated preferably to a 'big', a 'wing' and a guard, depending on available talent. Of course some of these players may have skills to do well at more than one traditional position...if so, great.
To this day, the vast majority of official team rosters at the college and pro level, as well as major sports sites, continue to use the G,F,C categorization...they do it for a reason: STILL that categorization comes closer to represent what actually goes on on the court.