I can totally empathise with your brother. I had a miserable experience with my PhD to start with - awful supervisor, huge amount of politics in the group and then I got pregnant which was the nail in the coffin.
My supervisor sounded similar - wasn't there very often but was very against me doing my own thing /exploring my own ideas, which I understand to a point, but a PhD should be an opportunity for you to develop your own research and not just be his/her lab technician.
I loved the science but became very disengaged as every time I read papers and suggested things he would dismiss them. There was also a real sense of degrading those PhDs who left science either immediately after their PhD or after their first post-doc, despite as others have said, the pipeline means that very few do actually continue in academia, and exploring other options is totally legitimate and should NOT be seen as failure.
I changed supervisor half way through (was the fourth person in 4yrs to do this so I had the reassurance that it wasn't just me) and it completely revolutionised my experience. Working with a different supervisor and in a new group gave me renewed love of the subject.
Your brother has done incredibly well to finish his PhD in this kind of environment. He won't realise it as everyone within his workplace will be conditioned to think otherwise.
I share the concerns of others that a young, ambitious PI in a highly prestigious institute will carry risks of similar pressures but it isn't necessarily the case, and it sounds like he has good vibes early on.
I don't agree with the concept that it you love the subject you will put up with whatever. There is no point breaking yourself or martyring yourself to the cause. But I also don't agree that a PhD is wasted if you continue in another career. There are so many transferable skills, he just won't realise it.
I really hope this post-doc is a positive experience after what sounds like a really rough few years. I so hope that your brother gets to continue in science as it sounds like he would be an asset to academia.