The carnist here claims that while veganism would solve problem X, something else would as well, and therefore carnism cannot be held accountable for causing problem X. The prime example: "We throw away 30% of all food, and starvation affects 10% of people. Carnism isn't causing worldwide hunger, food waste is"
Food waste will always happen, so you can forever just appeal to that. Even if we're down to the last person on earth that's affected by hunger, you can still say "Well, a truckload of milk went bad in 1982. If that milk hadn't gotten spilled, this gallon wouldn't be causing that guy hunger". This is just another deflection.
This is yet another example of lumping related things together and naming them under an aggregate cause. In this case, "food loss" is treated as a monolith that arbitrarily excludes losses due to the thermodynamic efficiency of creating animal products. Solving the problem of non-animal-agriculture-caused food loss represents actually a whole array of challenges across food harvesting, distribution logistics, education, and even freezer maintenance. Yes, if you aggregate all the losses (that arbitrarily don't include animal agriculture) together, you get a larger number. That's not particularly relevant when you're looking at super easy targets to feed everyone.
Starving an infant is only contingent on their need for food. Pushing people off ledges being immoral is only contingent on the existence of gravity. "Your honor, I didn't kill him. Gravity did!" You can always point to some other omnipresent thing as being the thing that is "the real cause" of anything, that doesn't mean that your committing some action, under those circumstances, absolves you. If someone else points a gun at someone and you pull the trigger, you don't get to say "Well if he hadn't pointed it at him, pulling the trigger for my own entertainment would be fine", just like you don't get to say "If we didn't waste so much food by these other methods, the collateral damage I impose on others by torturing animals for my own entertainment would be ok".
It's a weird argument to make that "while we could stop torturing animals for our own entertainment, why don't we instead attempt to solve every logistical problem ever in an attempt to keep torturing animals economically viable?"