Nothing ingenuous about stating the observable fact:  Since the end of the 16-2 start (which was 174 games ago) the Celtics have never played any stretch of games with anything remotely like those results -- with or without Kyrie.     They've been nowhere near a "56 win pace".  That's just not who this team has been.
If a player started his career hitting 12 shots in a row in his first few games, and then from that point commenced to consistently hitting at a 45% clip, how long are you going to wait before you stop giving much statistical significance to those first 12 shots when describing what kind of shooter that player is?
Time to let go of that red hot start to the Kyrie era.   Because those games don't paint an accurate picture of what the Kyrie era really has been like. 
A perennial playoff contender that averages 50 wins a year (after you've cooked the data) despite its 2nd best player being injured?
50 wins means nothing. Even 56 means nothing. The average champion is closer to 60 wins per season. We are not close to that for a whole season or back to back seasons. They need to work better as a team to gel, they need consistent rotations of the best players. Not tinkering playing bums or over playing FAs to be so they can be happy making money from some other team. The chemistry will never be there unless BS changes that part of things that he is in control of. That's what is worth beating himself up on.
It's funny how spoiled and entitled some fans have become. If you've been a Celtics fan since 1984, then you know that we didn't win 50 games once from 1992 until 2008, the championship year. A drought like that makes you appreciate teams that average 52 wins a year and have a legitimate shot to get out of the east with its second best player (and former all-star) injured and several of its young prospects still developing.
I'm glad we have a top-5 coach who is universally respected across the league, and whose teams have exceeded expectations 5 out of 6 years. 
Act like you know more than him all you want. It's not creditable.
C's by their own standards (not your's) is about winning championships. That's my hope.
It doesnt taking acting to know it if things are in plain sight. I'm pointing out a flaw that he should fix. Everyone makes bad decisions. Some do it over and over. Like BB struggles drafting but he is great in other areas. Does it make him bad or a coach I want fired? Of course not but he can hire different people to help him make better choices in the future. BS can get better people to help him in his flaws. 
As for creditable, just look at the season and the quote that gave us this thread for if we should question how he does things.
You criticized him for "playing bums," tinkering at the start of every year with the rotation and giving guys run just to keep them happy heading into free agency, as if you have any idea what goes into his allocation of minutes.
You don't know who's outplaying who and what units are working in practice, who's banged up or having personal problems (yes, there's an injury report but there are also internal things not released to the media), what the advanced scouting report says about the opponents, or how Brad is thinking strategically about future matchups with an opponent if he knows we'll see them again in the playoffs.
The best coaches change lineups from time to time. One minute Jordan Bell is starting at center for the Warriors, the next he doesn't see the court for 3 straight games. Is Steve Kerr tinkering, responding to circumstances or trying things out to see if they work?
What seems obvious to you in plain sight is subjective and reads like a know-it-all blogger, not someone with any real knowledge of the inner workings of a professional basketball team. 
Of course the goal is to win championships, but that doesn't mean there aren't a bunch of small failures on the road to success. Having the big picture in mind and a little perspective sure helps guard gets wild overreactions.