The sad truth is that any of those old 2-3 mechanic fights would be pretty trivial if released today. Raiders today are way better at execution than they were in vanilla/TBC. The same way that TBC raiders looked back on Rag as a simple and easy fight, today's raiders would look at Heigan as pretty simplistic.
The hardest fight in BT wasn't even Illidan. It was Mother Sharazz. And the whole fight was basically wear shadow resist and run away from the 2 other people when you get ported. It's embarrassingly simplistic and easy compared to even normal mode raids of today.