Let's compare WHM vs PLD

Protect I - WHM07 / PLD10 (+3)
Shell I - WHM17 / PLD20 (+3)

Protecht II - WHM27 / PLD30 (+3)
Shell II - WHM37 / PLD40 (+3)

Protect III - WHM47 / PLD50 (+3)
Shell III - WHM57 / PLD60 (+3)

Protect IV - WHM63 / PLD70 (+7)
Shell IV - WHM68 / PLD80 (+12)

Protect V - WHM76 / PLD90 (+14)
Shell V - WHM76 / PLD??

So Shell V for PLD99 won't be so absurd since the offensive spell Holy II is WHM95 while Holy I is WHM50 / PLD55 (+5)