I think the concept of 'formless' needs to be examined further. For example, at some point in history, things like radiation, gravity, magnetism might as well have been 'formless'; they have only been given 'form' when someone somewhere found a way to measure them. Nevertheless despite their lack of solidity, and our natural lack of senses that can sense them without machinery, they affect solid things and things that we do sense. Just because we haven't found a way to measure 'mind' doesn't mean it is 'formless' and can't affect the brain.
Another point is that Buddhist reality consists of the 5 aggregates, which have a variety of translations, and I suppose if one were to use the word 'mind', there would be a variety of ideas of which aggregate or combination of aggregates the mind consists of. So by using the word 'mind' in those arguments, there is a lack of clear definition of what he is actually referring to in a Buddhist context.
Finally I think the problem of "if there is no self, then what is being reborn" is a deep question that only advanced practitioners would be able to answer. It requires a deep understanding of the reality (or lack thereof) of one's self. I can't help you there. But the issue is not "If the mind is merely an emergent property of the brain then there is nothing to be re-born", but "If the mind is merely an emergent property of the brain and can't be re-born, then what is it that is being reborn?". He is assuming that it has to be mind that is reborn and if the mind is not reborn it can't be anything else. There's no further investigation about if not the mind, then what? Keeping in mind the point above that his using of the word 'mind' is not well-defined in Buddhist terms.