I think that while what you define carves out a nice lump of thingspace, it fails to capture the intuitive meaning of the word probability. If I guess randomly that it will rain tomorrow and turn out to be right, then it doesn't fit intuition at all to say I knew that it would rain. This is why the traditional definition is "justified true belief" and that is what Gettier subverts.

You presumably already know all this. The point is that Tyrrell McAllister is trying (to avoid trying) to give a concise summary of the common usage of the word knowledge, rather than to give a definition that is actually useful for doing probability or solving problems.