My understanding of Tam's position is that it's a big picture whole cloth 'What if...' hypothesis.
It doesn't 'follow the evidence' and there's no logical formulation which gets him there.
So we're left with it 'feeling like it makes sense' because... without experiencing Subjects, there's no knowledge or meaning.
The ontological step from No Knowing, to Nothing Existing To Be Known, thereby becomes what he would call absurd.
This gives Subject Experiencing a much more significant role in the fundamental nature of reality, which isn't a neat fit with our traditional ways of viewing reality, which are more neatly packaged in evidence and logic.
The big fly in the ointment is the evidence that non-conscious stuff existed prior to Subjects who could experience it. In order to incorporate this evidence, which he accepts, there has to be some underlying Subject-Object Relationship which is more fundamental than the Time relationship between the two.
It's an interesting way to conceptualise the world, but it doesn't use our usual tools of evidence or logic, so persuading anyone else is really down to it 'feeling like it makes sense' to them too. It also puts it outside the usual testing grounds of evidence and logic, and makes debate frustrating. There's nothing to anchor it, no grounds to debate on, no way to test it. As an argument it stands or falls on whether it makes sense to you.