My contention is that there is a very well established formula or blueprint that has been used by most of the top teams over time. There are variations and exceptions of course but I believe there are 3 key roles that are generally at the start of any good team:
Ball Handler/PG/Combo Guard
Wing - Primary Scorer
Big - With Skill
You can list team after team that fits this:
Johnson - Bird - McHale
Magic - Worthy - Kareem
Wade - LeBron - Bosh
Even more recent champions or finalists:
Holiday - Middleton - Giannis
Murray - Porter - Jokic
Curry - Thompson - Green
Curry - Durant - Green
Irving - LeBron - Love
Lowry - Butler - Adebayo
Most of these teams than have a secondary G/F scorer and a defensive big to round them out. This was Ainge and Parrish in the case of the 1980's Celtics.
Right now, the Celtics have:
Holiday - Tatum - Porzingis
This is exactly to the formula/blueprint. This is an improvement over last season with Smart - Tatum - Horford.
Beyond the current core 3 (not necessarily the best three), we are going with White and Brown. I would argue that Brown is best suited to be that secondary G/F scorer although White would not be bad in that role. Or White could be the primary guard in place of Holiday and could fit that role, although not as good. What this group is missing is the defensive minded big role. Most teams, even the really good teams, don't fit the blueprint exactly, there is always variation, but the blueprint still works.
Has the blueprint changed or evolved? I don't think it has. I don't think our roster balance is ideal. Tatum and Porzingis are awesome as the primary wing and big. But ideally, we really only should have 2 of Holiday, Brown, and White. Some are concerned that Brown and Tatum are not a good match. I don't see that as a problem but the balance is off a little. We kind of have 1.5 ball handlers (Holiday and White), 1.5 secondary GF scorers (Brown and White), the best primary wing in the league (Tatum), a very skilled big (Porzingis), but no defensive minded big, at least not in what is currently the core unit.
Now to be clear, "not ideal" does not mean not good. This unit is doing just fine, obviously. Brown, Holiday, and White are all very good players. It is working, there is just some overlap.