What an utterly awful proposal. Expect nothing less from B/R though.
I would probably not trade Rob for Ayton straight up, let alone Rob and our 6th man for Ayton. Yuck
Let's say you're Brad, and the entire medical staff comes up to you and says "Unfortunately we believe that Rob will be dealing with debilitating injuries for the rest of his career". Would you still think this is a bad trade? Maybe I'm a bit too high on Ayton, but I think you would need to at least consider it. He could be that elusive 3rd star, while also securing our big man for the future.
I think you are too high on Ayton. He can't pass, he's a mediocre defender, and he simply refuses to shoot the ball enough. His highest FGAs was 14.9 when he played half a season on a below .500 team.
In a vacuum I don't mind him. He's super efficient (almost as efficient as Rob) and is one of the elite rebounders in the league. But I just do not think he has the mentality required to be a third star, and if he is demanding max money, as I've seen reported, then I think he's mad.
I think Williams is the better player due to his defence and passing, and he would cost a fraction of the money that Ayton wants. Sure, if his condition was hypothetically debilitating, it would suck. But owing Rob $48m over the next 4 seasons is fine by me, even if he's limited to 25mpg or 60 games a season. Over the last two seasons, Ayton hasn't been much healthier than Rob.