Unfortunately, Occam's Razor can say whatever you want by fiddling the apriori probabilities. Here, the probability you need is how likely that theory is to be

Unfortunately, Occam's Razor can say whatever you want by fiddling the apriori probabilities. Here, the probability you need is how likely that theory is to be true - just because it could be false doesn't mean it's 50-50. If all the models show planet formation is messy, it seems reasonable to estimate its probability as much greater than 0.5 (note that even if it's 0.9999, they still could be wrong).