I look at the roster this way:
Combo PG: Smart, Brogdon, White, Pritchard
Wings: Tatum, Brown, Hauser
Bigs: RWill, Horford, Gallinari, GWill
This is 10 deep with players that can play regular minutes but most of the time, we are probably going to play with 1 combo, 2 wings, 2 bigs. To balance the roster, we need to swap a Combo for a wing (or just add a wing, that is OK too). We of course can play with 2 from the combo group and only one of Tatum or Brown (not sure if Hauser will be in the core rotation) but with this group, we end up a little light on shooting if we have 2 of the combos on the court together. But this would allow the minutes to be spread some.
TP for this. A lot of times we tend to pigeonhole players into the old positions, the 1, 2, 3, 4 and 5 and assign them fixed roles based on that. That's not how Brad thinks:
The new era of the NBA requires versatility to win, and the Boston Celtics are adjusting.
"I don’t have the five positions anymore," Celtics coach Brad Stevens said, per Kareem Copeland of the Associated Press. "It may be as simple as three positions now, where you’re either a ball-handler, a wing or a big.
"It's really important. We've become more versatile as the years have gone on."
https://bleacherreport.com/articles/2720250-brad-stevens-says-celtics-have-3-not-5-positions-now
With Timelord for example, He's not thinking that Timelord is is the only center on the roster, or even that he's a center. In today's NBA a lot of those old positions are anachronistic now where you have to fulfil multiple roles. Timelord is a big - a more traditional big that doesn't stretch the floor offensively but can come out to do dribble handoffs and set screens, and roll to the rim. Defensively he can defend other bigs, wings and some ballhandlers, and act as a rim protector against dribble penetrators. Meanwhile Al and Gallinari are stretch bigs who can post up and also pick and pop on offense. Al can defend out to the three point line against wings or ball handlers while Gallo is more of an interior defender, earlier in his career he was a lot more like Al. But they can fulfill those traditional big roles defensively as well, rebound the ball, play in the frontcourt. You can play them as the sole big if you have to against certain lineups. In fact Al was our sole big for years and defended the likes of Embiid and Giannis. Then you have GWill who can fill that big role in small ball lineups or play on the wing when there are traditional bigs on the floor, but also defend against bigs.
So with Brogdon, he can handle the ball and play the point if needed, he can play off the ball as a wing, he can defend wings if he needs to - just like Smartacus or Derrick White. It's not what their position is, it's what they can do on the court. Having four guards isn't really an issue to me - I see it as we have four guys who can handle the ball and facilitate the tempo of the game, and of those four three can also play on the wing and either shoot from the perimeter or attack closeouts and get dribble penetration.
So if you looked at it in terms of what roles they can play, you can say:
Combo PG: Smart, Brogdon, White, Pritchard
Wings: Tatum, Brown, Hauser, Smart, Brogdon, White, GWill
Bigs: RWill, Horford, Gallinari, GWill
Huge amount of versatility there, and many more different looks and combinations you can try to find some synergies and chemistry with and that you can possibly throw against an opponent.
I look at this a little differently actually. Where you list Smart, Brogdon, etc. as Wings in addition to Combo-PG, I don't consider any of these as wings. To me, if we had a line up of say Smart, Brogdon, Tatum, Horford, RWill, the result is a line up with 2 combo PGs and 1 Wing, not that Smart or Brogdon are a wing. This last season, our best line up was with 1 Combo PG, 2 Wings, 2 Bigs, but sometime you play with 1 wing, sometimes you play with 1 big, it is just the line up but doesn't change the natural position of the players. Another example could be Smart, Brogdon, Brown, Tatum, Horford. That line up is 2 combo, 2 wings, and 1 big. This line up does not make Tatum a big.
I use Combo-PG as a category where Stevens said ball handler. Hard for me to say he is wrong; I think my category is a little broader but we are still saying more or less the same thing. Someone else mentioned a category of "Swing" (PF-Wing combo). There are definitely players this applies to. Marcus Morris is a prototypical example of this in my opinion. Thad Young, others. I don't consider Tatum a swing though. He is a wing, one of the best wings in the league. To me, calling someone a swing is kind of a nice way of saying a tweener, not really either, in a negative way. Swings can be useful players, especially off the bench, they add versatility, but I would still rather have my principal wings be wings and my principal bigs be bigs.
I guess my thinking on positions has evolved from labelling a player with a position, to having positions that I see players as being able to fill due to their skillset. So rather then label a player as a wing, big or ball handler, I look at those roles and see which of them a player could fill. Because I think some players can adequately handle more than one role well enough to be tasked to do it regularly, rather than pigeonhole them into a position. Hence I think that someone like Smart can be tasked to play as a ball handler in certain lineups, or as a wing in other lineups. Kind of an evolution on the three positions - I see a number of really versatile players as being able to fill multiple positions. I agree though that there's no need to "have" certain positions - teams might play five out and never have a guy posting up or playing near the paint, so that would technically be a no-big lineup, even if that lineup included Tatum who happened to be the tallest guy on the floor.
It was really Giannis' emergence that changed the way I looked at things, because there was one year he played point guard pretty much the whole year. He has also played center, and obviously he has also played wing, and defensively he's been able to defend 1-5. I really feel that that's where the league is heading - positionless basketball.