Obviously if every vegan and vegetarian suddenly began eating meat again, then that graph would only increase in rate of change.

how? how can you know whether a farm can even expand to accommodate more production?

The problem is that populations still continue to grow and the number of vegetarians/vegans is neglible to overall growth.

any excuse you make doesn't change whether more animals were killed this year than last, regardless of how many vegans there are.

Less demand does factually translate to less supply and therefore less suffering.

this is not causal