The logical failure is on the part of the sola-scripturists, I'm afraid.
We’re not claiming anything not in scripture is wrong. That’s absurd.
We’re claiming scripture is true, and defines truth.
We’re also observing that just because something declares itself true doesn’t make it so.
We’re also observing that something which contradicts scripture is, by definition, false.
The Apostolic letters contain a written record of Apostolic tradition directly from the source.
If something contradicts scripture, it is clearly against Apostolic tradition.
If something isn't contained in scripture, it's value is indeterminate.
I'll stick with the promises and commands of definitive Apostolic tradition, rather then hearsay, inspiration, or revelation of dubious value.