Just some thoughts on this specific part of your post (more thoughts on the rest and in response to
aron later).
I agree with you that even if we could agreet that the church structure in the NT is just a
description, that does not mean that groups today shouldn't have that same structure. Indeed, as you have pointed out, they could simply say, "Yes, we know the Scripture doesn't prescribe our way of doing things, but this is how we've been lead and the Scripture approves it."
That, however, does not inherently lead us to the debate about who is "right" etc... That stance inherently allows that different "groups" may have different leading concerning structure (or lack thereof) and solong as none of them violate the explicit prescriptions, then all are fine. It is when groups want to superimpose their self-admitted
personal leading upon
other groups that the problem arises. If they self-admit the bible doesn't prescribe a structure, and that their group (and presumably all groups) are permitted by the Word to organize according to the Lord's leading, then there is no standing to criticize others: all these groups, with potentially different organizational structures (none of which contradict Biblical prescriptions) should co-exist without a debate on who is "right." As soon as a group begins arguing about who is "right" - they are implicitly arguing the Bible prescribes their structure, which they admitted was not the case... Follow?
More later...
Peter