They have a billion assets and could construct their team any way they want for the future. IDK why you are looking at their team rn and thinking this is their end goal, it isn't. It's merely a stepping stone for them to eventually trade IT and build through their Brooklyn picks as is, or to trade one of them for a star while signing Hayward.
And they won 50+ games, it's not poorly constructed. They ran into the greatest player in the world, a guy who might be the best ever. Utah lost to what might be the greatest team ever. You can possibly take away anything about either team in comparison to each other, other than nobody has a chance in hell unless they create a 3rd super team.
And if Hayward leaves, that's the reason why, because Boston has a chance at building a super-team and Ainge has shown he has what it takes to pull off that build strategy.