A meta-question: what’s the use in claiming something as “the first” (arguably or not)? The key question seems to be “is blogging an internet native & distinctive mode of communicating?”, not “did other net native modes precede it?” Is it an issue of origins (i.e. blogging = journals + Usenet) or ontological uniqueness? And how would it change your claims if someone argued with you to say that other earlier forms of communication were net-native first?
Obviously I don’t know the full context of your argument, but I don’t think “firstness” matters as much as distinctiveness – “blogging is net-native & distinct because of A/B/C,” not “blogging did this first.” Make sense?