Leeway was in Vanilla but (Latency had a part)

No, your statements that 0ms and 0ms = 0yds leeway, is flat wrong.

A attacking B while both are moving, A has 2.66 yds of extra reach.

If A has 0ms they see the extra 2.66yds. If A has 300ms, it appears to them as if they’re attacking normally, because while B is an extra 2.66yds away from them, the latency makes them look in normal range, because they haven’t been told how far B moved yet.

The leeway is fixed. Your latency affects how it appears.