Until your comment I had no idea per-impression real-time advertising bidding was a thing: https://en.wikipedia.org/wiki/Real-time_bidding

To add to that, 100ms-200ms is only the cutoff time to determine the bid winner from adexchange perspective. We still need to add the time for adexchange to notify bid winner + adserving load time for total ad response latency.

Not sure why you'd want to load ads synchronously. Surely you can just load the page with placeholder divs, and swap them out when the ads are ready? The extra jarring blink when ads arrive, should increase visibility anyway. And for the rest of us, that browse with ad-blockers the only change would be a quicker load time...