Teams are indeed loading up on size and it's not just big men. It's tall, long players at as many positions as possible. I remember the Bucks starting that philosophy in their drafting and also the Magic, to varying degrees of success (so far).
However, this isn't something easy to emulate. It's not necessary that difficult to add an Ibaka, Gasol, or Lopez later because they're serving in complementary roles. They're not required to be the stars or semi-stars they used to be. It is extremely difficult to find a Giannis, Embiid, Davis type. It's even very difficult to find a Gobert or Draymond who are limited offensively but are DPOY candidates every year.
I will say that if you're going to criticize the Celtics, they have more often than not neglected the big position as something they can fill in later for cheap, even though Horford was getting older and was an upcoming FA this season. According to them, their draft philosophy has been to take the BPA which generally is the correct thing to do. The problem is, now they find themselves with no depth at the position besides Robert Wililams who they only took last year and is extremely raw (sorry Dancing Bear).
As always with the draft, the picks you make 2-4 years previously shape what team you have in the present, not just in terms of quality of trade asset but also what you have to work with on the court. Without getting into the "they shoulda picked player X that year" game, I will say that they created an imbalance with their roster construction when they invested draft capital in Rozier, Smart, Brown, and Tatum, and then later signed Hayward and Irving.
The resulting team had redundancies at the 1-3 spot where established vets and young players were vying for shots/usage. Now, I'm not saying they shouldn't have drafted any of those players at the time, but I think now even Ainge would admit the imbalance caused issues this past season, with the culmination being our present situation where the only options for both 4 and 5 are scrap heap players.
I will say that some of the issues were bad luck. The drafts in 2016 and 2017 did not have early star talent in the big positions. If you look at 2016, the only accomplished bigs taken were 11 with Sabonis and 27 with Siakim (again, ouch dancing bear at 16).
In 2017, the only big you might take at 3 would be Isaac or Markannen, who are promising but I think everyone is happy with Tatum at that slot. Later guys taken in Adebayo, Collins, and Allen were good though, and the fact that we didn't have a pick somewhere in the middle of the draft that year was unfortunate as it was a deep draft overall and not very top heavy (not to toot my own horn, but I remember at the time wondering if it might be smart to try and trade the 1st pick for Sacramento's 5 and 10 and was roundly criticized - time will tell).
