Except you can not kill them in droves. You can kill cows in droves in the cow level, but the density of these high rune drop monsters is not that high.
For eample, you can average killing a single cow every 0.6 seconds if you are well geared at which point you do not need high runes as you already have enigma & infinity for solo farming cows with this kill rate. I assumed 400 cows and 240 seconds for everything (getting wirts leg and the cow level itself).
The density of these high rune drop monsters pales in comparison to cow density. Moreover, your kill speed will be less as you are still gearing up.
they really aren’t. I’d like to increase rune drop rate but make them bind to account. Encourages people to play the game to gear up in runewords, not buy them. But that’s a fairly drastic change. I would expect no less then a howling mob storming Irvine if it was even on the PTR.