PaulP: "substantiation that ENSO is not chaotic."
Even a basic double-pendulum or the square-root of 2 decimal integer sequence is quite chaotic. Any complexity is inherently chaotic. ENSO is clearly multi-chaotic. How is the plate tectonics constraining ENSO not chaotic? Roaming crustal plates do not produce crystal-order.
Another physics lens into Lunisolar ENSO-QBO is thermodynamics. The Earth-Moon-Sun three-body system is thermodynamically "hot", full of "non-thermalized" energy. If Earth and Moon collided with the kinetic energy of their relative motion, they would melt. Instead, thermodynamic temperature exists rather independently at multiple scales. At the human scale of molecular heat, Earth and Moon are "cold to the touch", closer to absolute zero than not.
This "near-absolute-zero" state allows delicate effects like ENSO and QBO to exist. Once again a Quantum Analog applies, in this instance Analog Quantum Thermodynamics, where before we touched on Analog Quantum Chaos. Make no mistake, these analogs are mathematically equivalent to classical microscopic QM, even though we are careful to distinguish them physically. They do combine in symphonic grand synthesis.
We give up a provincial bias toward our own timescale (and space-scale) in the science here, embracing the geologic timescale of Plate Tectonics and cosmic timescale of Solar System formation, to better grasp what is going on. These alternative framings allow us to evaluate the Lunsolar Forcing hypothesis from added perspectives. One prediction of the thermodynamics is that Lunisolar tidal energy and ENSO-QBO energy mostly exist at different spacetime scales, and therefore interact weakly. This allows ENSO-QBO mostly do its own chaos thing, free of strong tidal forcing.
Here is WP's LaPlace Article citing well accepted modern science [Celletti et Perozzi 2007] 200yrs after the great man's time-
"It is now generally regarded that Laplace's methods on their own, though vital to the development of (orbital mechanics), are not sufficiently precise to demonstrate the stability of the Solar System, and indeed, the Solar System is understood to be chaotic, although it happens to be fairly stable."