Just a bit of an RSD tweak so they can deal with blur/DR. Change the perk abilities from +1/+2 ab to +1/+2 enhancement.
If the AB bonus is applied to the weapon, then it will pierce DR up to that number regardless of enhancement.
Both should apply their respective attack bonus increase on the weapon, enabling it to bypass X/+1 and X/+2 for sharpen and fervor respectively. If these are not applying the bonus to the weapon, there is a bug.
Changing them to enchantment bonus would only add a damage increase as well. Whether that is desirable is debatable, of course, but the implementation we have already satisfy the original suggestion.
Playing an RSD I can confirm that the AB+1 is sufficient for bypassing DR. Do remember that there are also other creatures such as Umber Hulk grubs and Lycanthropes that also have secondary DR abilities of a higher tier.
On a side note using Fury & Focus together, one doesn't show the AB increase on the character sheet but it does show up in the combat log.
You can also have weapons with both attack bonus and penalties so they cancel each other out AB-wise but still cut DR :)