This assumes that P(\mathrm{suff}|\mathrm{omni}) < P(\mathrm{suff}). Why do you get to assume that? It’s readily clear in the vegetarian case: we know that typically, people have control over what they buy, that they usually mostly buy what they want, that there are few good reasons for a vegetarian to buy meat, and so on; i.e. that typically, being vegetarian means that you’ll buy less meat than the average person.
But none of this is given in the case of God. We have no relevant background knowledge beyond God’s nature. The entailment from this to the above assumption is not trivial, so at least the argument has to be made. First of all, God’s omnibenevolence alone is clearly not enough: a perfectly omnibenevolent, but completely impotent and maximally ignorant deity may be neither able to avert suffering, nor sufficiently knowledgeable to see that what they’re doing is causing suffering. So God needs both a certain power and knowledge to act on their intentions. That’s fine, of course: the God in question is generally thought to be both omnipotent and omniscient (and omnipresent), so there ought to be no trouble on that front (although it should at least be acknowledged that we’re at best doubting the tri-omni nature of God, not omnibenevolence on its own).
But does this nature suffice to entail that P(\mathrm{suff}|\mathrm{omni}) < P(\mathrm{suff})? (‘Omni’ now referring to the conjunction of the three omni-characteristics.) Again, I don’t see that it does. First of all, as already noted, starting out the argument with the admission that some form of ‘God’ exists significantly weakens it: while it would be fallacious ad hoc reasoning to appeal to ‘mysterious ways’-type arguments when the question is God’s existence, if that question is settled, then we should indeed expect the actions of a being of vastly greater power, knowledge, and understanding than ourselves to be largely incomprehensible, and indeed, as impossible to make sense of for us as it is for a dog to understand calculus.
But even beyond that, there are further mitigating factors. One is that even a tri-omni being is not free from constraints. This is the lesson of the free will defense: just because the absence of suffering is God’s intention, it doesn’t automatically follow that it is in God’s power to bring this state of affairs about. Furthermore, as @Max_S also notes, benevolence doesn’t necessarily entail the prevention of all suffering: the dog owner that brings their dog to regular vet visits may be the more benevolent one.
So is it the case that P(\mathrm{suff}|\mathrm{omni}) < P(\mathrm{suff}), even given constraints on God’s power, the possibility of necessary suffering, and our imperfect understanding of God’s actions? It certainly might not be. At the very least, further argumentation is needed to argue that it is—which you have consistently declined to provide.
This also fits very well with the available evidence: evidential arguments from evil, as they are found ‘in the wild’, start with arguments to the effect that some particular kind of suffering is very unlikely, given that there is a tri-omni deity—which then grounds the inference from observing that sort of suffering to a reduction of credence in the existence of that deity. So the observed evidence—i.e. the arguments that are actually being made—is much more in line with the idea that additional argumentation is needed than with the idea that any observation of evil suffices as countervailing evidence. But of course, this particular kind of evidence has so far failed to nudge any assigned credences, and will continue to do so.