I suspect deep learning researchers have no real incentive to use the minimum amount of data sufficient to get their thing working. The worst case for them is i

I suspect deep learning researchers have no real incentive to use the minimum amount of data sufficient to get their thing working. The worst case for them is if their model underperforms because of insufficient data instead of something truly DL-related, so they use as much data as they have/can handle. It could still be that you're right, but I wouldn't rely on those kinds of published numbers.