The habeas relief talked about here is not about a criminal prosecution, so your predicate doesn't seem to hold in the first place. Secondly, there's an established protocol for interviewing people detained in a war zone and mirandizing etc (See e.g. the current prosecution of Abu Khattala https://en.wikipedia.org/wiki/Ahmed_Abu_Khattala , who got mirandized only after intelligence interviews etc., by a clean team.). Simplifying you can interview people before mirandizing, you just can't use it in front of court.

FWIW, so far the civil courts have a way higher success ratio than the absurd military courts system. It's not that hard to convict people on the basis of material support charges etc.