I'll say I don't like Brad's coaching style nor his offensive philosophy. I'm not sure he's actually cut out to lead a team to great success. Sure, he can get a team to over-achieve to a certain point, but there are serious red flags about his ability to lead multiple stars. He also seems a bit inflexible in adapting to the talent he has, and at times tries to force the proverbial 'round peg in square hole'.
But Brad certainly did not invent small-ball. He does cling to it a bit too much, though. That's partly Ainge's fault for not getting this team some better size, but Brad hasn't always best utilized the size he has been given, either. I do agree that Brad should be on the hot seat, but I'm not sure he actually is.
Do you have any examples of that? It certainly seems like he's done a great job of changing the system based on talent (having Horford as a high-post distributor, giving IT everything he needed to have one of the best scoring seasons ever, playing to Kyrie's strengths with with more iso, etc.)
He's not going to build a system around role players (or late first rounders that may be role players in a few years if they improve a lot), and he'll ask role players to adapt/expand their game to fit better, but that's really what you want with role players. You don't create an entire second offense for the 10 mpg that a min-contract-level-guy plays, you either get someone else that fits the system better or ask them to adapt.
Having the team continually jack up threes when they were off in a given game was one glaring mistake. It's like he had no other pitch beside his fastball. Also, not using Horford more as a 4 was another big mistake. He had three wings with egos to satisfy, which is Ainge's fault, but I felt he didn't adapt well to it at all. He totally mishandled the Hayward situation.
Stevens failed miserably last year. He could get the team to meet expectations. That's a big warning sign, to me.
If your shooters aren't super streaky (Smart is, but most of our other guys are not), then abandoning the best strategy based on things not breaking your way is a bad idea (and that's ignoring that perimeter shots not going in means defenses will pack the paint more, making it harder to score inside). The change that we needed in that case was going to the hole and finishing through contact or getting to the line, but we had no one that was capable of doing that consistently. I'm hoping that Tatum and Brown are able to this year (Kemba also gets to the line more than Kyrie, which is an improvement), but if no one on the team is capable of it then I wouldn't blame Brad for having guys take the open shots instead of going inside and getting destroyed there
As for Horford playing the 4 less, there was just no one else to play the 5 for a lot of the year. Baynes was struggling with injuries, which left the only available options as... Theis and Timelord? Neither was a good option, and neither had a better effete on the game than going to small ball with Horford at the 5
Did Stevens have some effect on the roster construction that led to those issues? Yes, I'm sure he did. But he wasn't 100% responsible for the team's struggles, and a change in philosophy would only have changed what people complained about (like if he played Horford next to Timelord/Theis more, it would be not working with what he had available rather than going small too often, or if he had guys going to the rim just for them to get stopped it would be for not enough ball movement, etc.)
The fact is that last year's team was not as good as we thought they were gonna be. No amount of coaching was gonna fix the two (in my opinion) biggest issues: getting to the rim to finish through contact/get to the line, and big man depth for when Baynes was hurt