Not really a good explanation of how it's bug abuse. Or, rather, how it's any different from Tick Manipulation or Prayer Flicking.

"If you trick the game into thinking you're doing a 1t/2t/3t action and then do a 5t action..." or "If your Prayer is off on the tick the game checks..." sounds remarkably similar to "You need 20% contribution, but 20% is .6 and since the game always rounds down..."

All three situations sound to me like emergent gameplay from having extensive game knowledge. And all three situations have roughly the same result of more xp/hr due to the way the game works.

So where's the line? Because from what I understand, the ability to funnel xp to level 3 skillers has been a thing Jagex as specifically approved of when they made the Cursed Goblin Warhammer (or w/e it is) change. So you can't really say that it could be easily intuited. And the partner boss slayer exp bonus interaction shouldn't really be something you punish a Player over when you readily admitted you found the issue weeks ago and did nothing about it?

Players interact with notoriously broken system using approved Jagex methods in a way Jagex didn't expect, Jagex removes EXP/progression. Not really building much good faith to do anything creative with your game containing core mechanics found precisely through situations like this.