Why not just put a motion to a general meeting to adopt whatever set of bylaws you want? Then, if it passes, that great. If it fails but was supported by every owner except the developer, you then seek an order from the Tribunal to give effect to the failed motion on the grounds that objection to the motion is unreasonable.
I assume NSW has a provision for doing that. I am familiar with the ACT law, which does. In the ACT the Tribunal does a merits review of the failed motion. That is, it looks at the proposal and determines whether it would have been reasonable and preferable for it to have passed. The Tribunal does not determine whether the person objecting was being unreasonable. It is only concerned with determining what the best outcome would have been.
If your proposed by-laws are identical with the model bylaws or closely modelled on them, you can argue that is clear evidence of their reasonableness. If the argument is uncomplicated and you have demonstrated by the vote that every owner except one is in favour, you should be able to get a good result out of the Tribunal at little cost without needing a lawyer.
I suggest that putting the motion to a properly notified general meeting is the first step. Make sure you have every owner take part, in person or by proxy. I think the Tribunal will want you to demonstrate via proper general meeting minutes that the motion has unanimous support (except for the developer) and that you attempted to amend the bylaws via the correct process before seeking a Tribunal order.