I think the creatives can be 'blamed' for casting Billy because no one casts themselves. However, I'm not sure I agree that the issue is as simple a "he is only allowed to do what the production allows him to do". Part of the perception of what is going on here is that it seems like the Director of Billy Porter in Cabaret is not Rebecca Frecknall, but Billy Porter - mainly because Billy Porter's choices do seem to be a complete departure from many of the original choices and concepts.
And when you get 'a star' sometimes you have to accept what they want to do, otherwise you don't get 'a star'. If these were Rebecca Frecknall's choices I think she should be throwing Billy Porter a bone and put a social media update that Billy is doing what they wanted him to do, because he is the one getting the blame for it!
I wonder if what Billy Porter needed to be successful in the role is a combination of 1. It should have been 6-10 years ago when he was in better vocal health and peak fame 2. Much more heavy handed 'handlers' that can try and lead him to be more careful about what he says in public appearances, reminding him that the goal should be to be liked and forward his career not to speak his mind freely all the time (it sucks, but this is the world we live in) 3. A different production, such as a Jamie Lloyd take or another more radical take that would have helped people accept his choices 4. Not being a replacement and following people like O Peck and A Lambert might also have helped.
On 3, I kind of accept the more I think about it that of course people might find it a little at odds with the setting and character for someone to say 'thank you bitchesessss' and metaphorically snap his fingers about. But the production and context is everything - for example, Nicole Scherzinger is definitely not playing Norma Desmond in the 1950s in Sunset but it works within the context of the production and direction. For this take on the role, he needs a production that lets the audience suspend a little disbelief about the time period and not be taking his performance so literally.
But I also really think the vocal health is also what's killing him a lot - because if he is going to go for a take on the role that employs a lot of vocal improvisation and vocal pyrotechnics if he doesn't actually have the voice to support it I think it might come across to some not as a dynamic expression of his inner emotional world (which I think was the intention, for example in 'I Don't Care Much') but as someone who is unpleasantly wailing, struggling, straining.
Give me claws and a hunch, just away from this bunch.