Let's clarify here:
In 2.0 WHM could take 5 abilities from the following:
Ruin - Useless
Physic - Not worth taking unless you wanted a different casting animation for whatever reason.
Virus - Mandatory #1
Eye for an Eye - Mandatory #2
Surecast - Anti interupt, this was very niche for specific situations back then. #3
Swiftcast - Mandatory #4
Thunder - 210 potency over 18 seconds with 30 potency upfront for a total of 240 potency. This dot had better GCD efficiency than even Aero II. Mandatory #5
There was only one reason not to have Thunder loaded. And that was patch 2.1.
I think I've covered all the bases? I'll stop derailing the thread with that =(