I don't believe his intentions were to cause any rifts because quite clearly, Stevens, like a lot of coaches in the NBA, can do everything right up to a point and then out of no-where decide to get cute and make a costly decision because of pride, inclusion, or an ill-advised idea that James Young will prove useful. I am literally asking myself if Stevens is aware that the trade deadline has passed and James Young's services will no longer be required here in Boston.
IT knows this is his team and it's a player's league. He's the talent here, we NEED him. He'll get away with this slew of criticisms based on the fact. You can feel the frustration as there is a lot of pressure and faith in him from top down in the organization and they want him to earn his money.
LOL. TP.
Regarding IT, my suspicion is that he may be starting to see—as Ray Allen once did—that he is, in one sense, just a single cog in the complex machine that is Danny's Master Plan (hereafter referred to as the DMP).
This isn't to say that Danny doesn't genuinely care about IT, or Ray, or any other of his players; I think he does.
But individual players ultimately play second fiddle to the DMP, because Danny's goal—in fact, his job description—is to win titles, which necessitates making the team as good as possible for as long as possible in each era. The New Big Three era is over, and now he's building the next era. He pulled off a great move getting Stevens as coach, and a big heist in getting IT on the cheap, and I think the quicker-than-expected success over the last couple of seasons presented an opportunity to get even better even quicker, so he signed Horford, then tried like heck to complete the nearly overnight makeover with a KD signing but came up just short.
So for now, he's fallen back on "keep the team good, competitive, and improving" until he can make his next big strike. It didn't happen at this year's trade deadline, but it could happen on draft night, or over the summer; either way, Danny's main concern is maintaining the team's upward trajectory while maintaining roster flexibility so he can strike at the right time and in the right way—that is, making the right moves to ensure as large a title window as possible, certainly longer than the title window of the New Big Three era.
I'm sure that, in Danny's ideal world, that window would align perfectly with IT's rise to stardom (and even the remainder of Horford's prime), but if it doesn't, his sentiment is probably, "Oh well." He's building something, which means that from his point of view, it doesn't matter if Player X is part of the building's foundation, part of its support structure, or the capstone—what matters is the overall building and how that turns out.
That can rub players (and fans) the wrong way, but that's the way it is with Danny. In the DMP, no player is bigger than the team or long-term success.