With the exception of SoC and an insignificant AP benefit on SoR, paladin abilities used to be single-coefficient. They either benefited from SP or from AP. This was pretty bad for ret since it only had AP. Then two things happened. The first (not in chronological order, just order of me thinking them up), was awesome and was called Sheathe of Light. The second has no name and it ruined everything, it is the addition of AP benefits to just about every paladin offensive ability.
Back when ret had no SP the second thing made sense. But now ret has SP, from AP, so adding AP bonuses just means that ret gets to double-dip. Sheathe of Light is great, keep it. But...
What if abilities benefited only from AP or SP? The problem isn't sheathe, the problem is that everything was changed to allow ret to double-dip. If SoR was only SP, it could have a much higher SP coefficient. Judgements can be pure SP (as they used to be), since all specs have SP from somewhere.
Anyone that needs SP either wears SP gear (holy) or gets SP from other stats that they wear (prot and ret). Anyone that needs AP either wears str gear (ret and prot) or they don't need it (holy).
Weapon-based attacks: AP (from strength)
Shield-based attacks: BV (from strength)
Spells (including heals): SP
There, everything is fixed. Now Blizzard can buff back up SP coefficients while removing AP bonuses on most spells; leaving ret unchanged and the other specs stronger.