I think it all comes down to fighting style.
True, your scythe is targeted, it it also causes you to lose balance.
The rune on the other hand, if memory serves me, activates every few seconds automatically.
Plus, preparation is key.
If you are in the same location as your opponent, then not having a diffusion cloak isn't a big deal.
However, if you intened to move, and you know your ankh rune has stripped your spirit defences, then you should know to put them back up again as soon as you move.
You opponent, however, might have been caught unaware by the rune, and/or may forget to put that all important cloak back up, which gives you the advantage.
Each little battle you win brings the overall challenge closer to your hands.
Written by my hand on the 25th of Paglost, in the year 999.