See my other comments on OLOFOB, while contrary to your thesis, sola ecclesia fails to produce the unity RCs imagine Rome effectual produces, and which is not the same unity as that of the early church, as it does not have the same basis, and Rome's gospel preaching is manifestly far different from the regeneration we see it effecting in Acts.
The Watchtower society also claims to have the unity of the early church, and in doctrinal conformity it surpasses Rome, but as in Rome, its based for unity is upon implicit submission to an infallible type of magisterium, and its authority is limited to their flock.
For Rome to claim supremacy then its basis cannot be her claim to a supreme unity that was like that of the early church, as not only did the latter unity have a different basis, but Rome also fosters much disunity, and in addition every church can teach doctrines and can require consent and claim unity under it, and which can be more conformist than Rome.
Thus the real argument for Rome as supreme is that her claim alone is warranted, based upon historical descent, stewardship of Divine revelation, and being the inheritor of Divine promises, all of which are an interpretation in competition with others. And thus my questions to you which you have yet to affirm.
I don't think Moses or the Rabbinical school is sola scriptura at all. In addition there is the oral torah/written torah.
And as in Catholicism, the mere tradition of the elders was taught in their oral tradition as doctrine, and thus the Lord reproved them by Scripture, (Mk. 7:1-16) and He established His claims upon Scriptural substantiation, and thus the church began in dissent from those who sat in the seat of Moses.
Under the Roman model the Lord would have been rejected for so reproving them, and thus would be was opposed as not having their sanction, as Rome has done to others who corrected them.
I've described the Church before, in this context it is Sacred Scripture, Sacred Tradition and the Magisterium. I would describe sola ecclesia as an individual using sola scriptura - the individual is the church in determining doctrine - all by him/her self.
And Jehovah's witnesses is sola scriptura or close to it. It is another example of sola scriptura not working.