The razor is commonly misunderstood.
William of Ockham objected to his fellow theologians inventing things out of whole cloth (like dark matter question mark). That’s the point, not that a simpler explanation is more likely to be true.
The common understanding would have us believe that creationism, being simpler, outshines evolution, or that there is no such thing as a color revolution because the simplest explanation is that the mass protests are earnestly aggrieved locals.
Yours is a common misunderstanding, as well.
Occam's Razor only kicks in when the hypotheses have equal predictive and explanatory power.
The MOND hypothesis does NOT have equal explanatory power with the dark matter hypothesis. As such, Occam's Razor is not relevant.
Maybe you can point me to the "equal predictive and explanatory power" bit in William's writings.