That's basically the same math, man, with basically the same results. The difference in numbers is probably cause I did mine by hand.
red pot obviously scales better with a second PD. By about 19 damage per second before resists.
green pot obviously scales better with a MBR. I'm just about as lazy on this one, though, so w/e.
Regardless, being 1k more expensive just isn't enough on its own to justify saying "this is bad on Kog" when considering your last offensive item. 1k isn't hugely significant compared to other considerations, such as what your opponent's survivability looks like or if you bought an early Madred's razor for dragon control.
I'll grant that it is probably a situational pick, but situational != bad, by any measure.