I think I’m using the term correctly. The use of a mechanic “by a player to their advantage in a manner not intended by the game’s designers.”
https://en.m.wikipedia.org/wiki/Video_game_exploit
The key words there, IMO, are “advantage” and “intent.”
Does it provide an advantage? Yes, 25% haste is a MASSIVE advantage against PvE content.
Was it intended by the original developers to be reliably stacked up to 25% for boss fights? For me the answer is clearly no.
Do I have a link to where this was explicitly stated? No. Can I read their minds? No. But common sense allows me to state with 99.9999999% confidence that it was not intended that a level 45 item be the most powerful item in the game, which, when stacked, has the effect of increasing an entire 5-man group’s damage by a whopping 25% for four minutes.
I am 99.9999999% confident that it was unintended and that it would have been nerfed immediately had this technique become commonplace in original TBC.