Even leaving out the whole "experimentally verified" thing, parts of a system can have longer description lengths than the whole system by breaking symmetries in what you include. Which means that if the system has a description length distributed according to the simplicity prior, such a part doesn't. So it's not that you just shouldn't use the simplicity prior on everything, it's that you can't.
If you're saying our observations can be complex even though the universe is simple, you're essentially taking the first horn of the dilemma in my post. This means you cannot use Solomonoff induction to figure out the correct quantum physics, because Solomonoff induction works on the input stream of bits that it sees, not on the "universe as a whole".
You're about to flip a quantum coin a million times (these days you can even do it on the internet). What's your estimate of the K-complexity of the resulting string, conditional on everything else you've observed in your life so far? The Born rule, combined with the usual counting argument, implies you should say "about 1 million". The universal prior implies you should say "substantially less than 1 million". Which will it be?
EDIT: Wei Dai's comment explains why this post is wrong.