I work in mobile ads, and for fun, i injected 50ms, 100ms, 250ms, 500ms latency in an experiment. The results were not as dramatic. 500ms had less than 1% impact. 50ms looked almost positive (didn't wait enough to have it statistically significant). This is 2018. Results are rather nonlinear, and different formats with different latency requirements had different results (like formats lending themselves to advance preloading would not be impacted at all even at 500ms, but ohers which had tighter UX requirements would).

I realize results are context-dependent, this is why everyone should make their own conclusions from their own analysis. You might have bigger bangs to make than shaving off some latency.