You can’t use that. That’s Sola Scriptura unless you have some other authority.
We all agree with the authority of scripture. What is in dispute is your claim of sola scriptura. All of your post point to the authority of scripture but not to the sola part of your claim. All your circumlocutions do is highlight that nowhere in scripture does it claim to be the sole authority. If there were a passage in scripture that unambiguously made such a claim you and others would be posting it in letters three miles high. You cannot do so because such a passage simply does not exist.
No it's not, it is simply a (semi) quote from the Bible....like THIS IS MY BODY...which we also believe. That, however does in no way indicate that ONLY quotes from the Bible can be considered.