I agree with Guaran, and I would support his suggestion.
The reward system for killing the guardians should not be changed.

As Chib already mentioned :
What applies for drain strike , applies for spiked scales too.

There are more rewards for visiting Drulkar`s cave/ using rune of ascension:

- Dimensional pocket (passive)
- Drulkar`s wings (pasive)
- The Lunus/Helian crystal
- Flame burst

Maybe one of those can take the place of drain strike/spiked scales,
if its not possible to install Guaran`s suggestion.