In not here to argue the merit or sins of spell batching in classic wow, however something about it in this classic WoW feels off a bit.
This has lead me down the rabbit hole in a couple of different ideas on what may be happening in classic.
As an outside observer and a student of history we know that vanilla ran in a different kind of server hardware architecture and additionally ran in its own bespoke system.
Classic is not like this; it’s very much likely to be a modular system like Microsoft Azur, a very scalable and robust system that has some great advantage, but all things are not equal.
Many things have changed server hardware and system side; back in actual Vanilla Blizzard potentially had a few things actually run client side because distributed computing was a thing back in those days. (Thank you Microsoft Windows NT servers)
Does not mean they did this but it’s very possible and allegedly this was so until some time early TBC when a certain warrior was hacking his client to alter his auto attack speed to produce more swings and more rage as a result.
It’s such a subtle hack that if he had never been competing in top end arena then odds are would never have been detected.
Needless to say he did get busted and things were altered a bit, but I never noticed any player side effects in TBC as a result of their security changes.
Fast forward to Wrath, here again we were still using “Vanilla batching” and everything was fine; broadband connection was now common place and yet the game mechanically felt exactly as it always had since vanilla.
Point is Vanilla to Wrath felt EXACTLY the same, and always felt good.
By the time wrath was launched internet connection speeds for most players was considered excellent and yet the game felt the same.
Fast forward again to cata, New batching system (more faster channels), and the game played roughly the same.
In all of those years never did I ever observe the kind of behavior displayed by spell batching as I see in classic wow, nor did it behave this way in TBC or Wrath. (Not talking about 2 mages sheeping each other or two rogues sapping each other) Additionally I never observed leeway act as it does in classic wow back in Vanilla, TBC or Wrath.
I strongly believe that ends are what is important here and arbitrary numbers like 400 ms batches are meaningless, and the only thing that really matters is mirroring the original game.
Do you need another reference point? Perhaps a new and reliable source or two?
Start up a new TBC or wrath of the Litch king server and see how it feels and plays.
PLEASE trust your memory of a class you the developer once played. Your muscle memory will not lie too you in the way the numbers and hardware changes can.
Please consider this thought experiment because quality game play is of the highest importance to everyone; including you all at Blizzard.