Leeway is still in retail, with the exact same formula it has always had.
Leeway in Vanilla.
Leeway in TBC
Leeway in WoTLK
Leeway in Cata
Leeway in MoP
Leeway in WoD
Leeway in Legion
Leeway in BFA
Leeway in Shadowlands
Leeway in Classic
Leeway on the BC Classic Beta
All of these are the exact same. Leeway has not changed or been modified at all in 15 years. Tauren hitboxes have been normalized, and the WoW servers were moved to a 10ms batch cycle instead of a 400ms batch cycle when the WoD prepatch hit.
Here are some links, you can see that melee leeway was the exact same in Vanilla, MoP, and BFA. It didn’t change between any of those expansions, nor has it changed after any of them.
turinpt comments on To all of those who claim Melee leeway wasn’t in vanilla (reddit.com)
Melee Leeway is a BFA Mechanic? | Classic WoW Discussion - YouTube