The issue goes deeper, as the mandate to discern and teach truth is one thing, and the basis upon which it does so is another.
And under the premise that the church is the supreme authority you have different churches competing with each other for the title of the one true church, based on the premise of assured infallibility. And which (again) in the case of Rome effectively rests upon her own deceleration to be so, infallibly claiming she is infallible whenever she speaks in accordance with her infallibly defined criteria, and which does not necessarily render the reasoning and arguments behind them to infallible.
And which is not what the Scriptural mandate to discern and teach truth presumes, but which is established upon Scripture being supreme and providing the warrant and attestation by which truth claims are established.
I’d really like to respond to this hash, but I just can’t figure out what you’re trying to say....