You present a false challenge, as Dyad would also be One via two monads as well, so doesn’t possess exclusivity in being stated as a potential whole, which is exactly my point, it is potentiality we are discussing.
Two can be specified as all, such as the Matter-Antimatter universe, without conception of a third intrinsically necessary for total wholeness. An Egg and a Ovary can be whole.
Two, Dyad, is a serialization of One, Monad, a further specification upon Monism, with characteristic.
If I make a statement Horse, it is by default Dyad at least, but you can’t prove it is Triad without syllogistic examination. Is it a “white horse” as a further possibility isn’t under consideration, as the sibject-object consideration isn’t under consideration, it may be albino, or in the dark, viewed in ultraviolet, or the “observer” may be blind, studying it via tactile senses. We are only certain of Dyad, not Triad.
This is the basic underlining of syllogism, all syllogistic structures must follow, and so is built into every proof, and therefore cannot be disptiven, as it is part and parcel to every proof. What is not part and parcel is your own flight of fancy regarding Triadism. It can be, but isn’t ever assertain. Is one ever certain if The Son, The Son, and the Spirit as same qualities experienced at any given time, or are they experienced in degrees separately? Are we engaging the Subject-Object sceptism in rationalization that differently experienced parts are a holistic whole? How can we ever be certain, given human fallacy? I hold to the trinitarian creed but am also a Doubting Thomas in all things.