One problem with your proposed DH8 and DH9 is that sometimes they just aren’t possible. Sometimes people are just wrong and no update is necessary. The rest of the hierarchy is always possible regardless of the strength of the argument. DH8/9 not so much.
As I mentioned, unless your opponent is stupid or trolling, in which case any level of engagement is probably wrong, there is a high chance that there is something to their claims, limited in applicability though they might end up being, so DH8/9 (and maybe higher?) are worth at least considering.
One problem with your proposed DH8 and DH9 is that sometimes they just aren’t possible. Sometimes people are just wrong and no update is necessary. The rest of the hierarchy is always possible regardless of the strength of the argument. DH8/9 not so much.
As I mentioned, unless your opponent is stupid or trolling, in which case any level of engagement is probably wrong, there is a high chance that there is something to their claims, limited in applicability though they might end up being, so DH8/9 (and maybe higher?) are worth at least considering.