I'm not saying it is a purely empirical argument, hence my extensive mention of metaphysics. There are many, many, many theories that can match existing observa

I'm not saying it is a purely empirical argument, hence my extensive mention of metaphysics. There are many, many, many theories that can match existing observation, such as superdeterminism or superdeterminism where there is a human-form God right outside of our causal observable universe that is using some magical force to determine where all particles are. The principle of parsimony, imo, favors an everettian explanation - and constructing larger contraptions with QM effects puts increasing parsimony pressure on why observers like humans are not simply getting entangled with the system they are observing when we see 'collapse.' The mathematics of QM does not describe collapse or how that occurs from wavefunction evolution or why observers are relevant.