When the pre-wrath patch went in, Leeway became very noticeable to many players. I remember players reporting it on the pvp forums again and again. And even Bashiok was posting trying to figure out what was going on.
It could have all been coincidence or something, but suddenly the idea that "everyone’s hitbox’ is really huge was being discussed. I don’t know if it was the internet happened to speed up at that time, or data centers for wow got some boost. Or there was some other change at that time like Leeway range was increased. Bashiok mentioned that that patch did touch rogue hitboxes, and they were hotfixed. It was also in this patch there were visual bugs as to the circle that highlights selected players, some classes they were crazy huge, I think it was only visual, but is further evidence that devs were touching hitboxes and possibly leeway around this time.
As far as my own anecdotal evidence, I used to run flags in WSG. When the pre-Wrath patch hit I started getting hit from long range by melee. I played regularly against the same players for 2 years. Now suddenly I couldn’t kite ones I ran circles around before. In the WSG flag room, there’s the ramp leading up into it from the tunnel. I could be at top of ramp running, and getting hit by people at bottom, that’s how out of whack Leeway became.
It’s possible when they built Classic they took later values from 4.2 and it had this too long of Leeway.
It also is possible that the new spell batching system is causing the leeway window to remain open for too long. Or even that Leeway is triggering twice per character, so it’s like 4x Leeway! Like characters are being perpetually read as moving, because the game only updates actions every so often, so the ranges are wide for too long. It’s like a buff being applied to the players so long as some movement input was registered.
Also, my understanding of leeway is that it isn’t the attack range is increasing. It’s that there is a circle around the player all the time, and the player might be standing anywhere in that circle, therefore, any attacks register on that player within that circle. When Leeway kicks in on one player, that circle widens and now you imagine there’s dozens of positions the player may be standing on for terms of being hit. In Classic, the Leeway range also increases when the attacker moves.
I think maybe in Vanilla up to pre-Wrath patch, the Leeway range didn’t increase for the attacker. Or, it was bugged and Blizzard thought it was working that way but it wasn’t. It’s very possible that on either side, the attacker or the attacked, that increased hit area of possible positions didn’t mesh with the game world properly, and thus it was bugged in that way.
Finally, maybe cause of bad latency Leeway just didn’t go off back then. Like maybe the on-off for it was missed most of the time, so only in some matchups players would notice it at all. I played cross country and definitely experienced difference in movement and positioning with players from Pennsylvania, or Alabama, or Texas, or Montana, or California. Then there were the players who were on wifi from their neighbors. Some of them were gladiators, their latency definitely did help them, even though they were tenacious players too. Now Leeway might just be grabbing up everyone.