I mean only that the description I sketched (which might be seen as referring the the idea of "mathematical universe", but also deconstructs some of it, suggesting that it's meaningless to insist that something "is a mathematical structure"), isn't saying much of anything, and uses only standard ideas from mathematics; in this sense the idea of "mathematical universe" doesn't say much of anything either (i.e. is trivial).

It might be a useful point to the extent that understanding it would banish useless ways of metaphysical theorizing about the physical world and free up time for more fruitful activities. So, my comment is unrelated to your point about decision theory, although the simplification (back to triviality) may be useful there and probably more relevant than for most other problems.