Books give you infinite use of a spell... I don't see how making scrolls scale properly would make them "too powerful".
Are healing potions "too powerful" because they scale and heal better than Restoration?
Maybe we should make food heal for only 5 flat health instead of 5-10% too.
While we're at it, Special Arrows should only deal 10 damage without scaling to not deter the player from using normal attacks.
I'm sorry, but your excuse is a load of...
You don't find a scroll per barrel last I checked. Hell, you find more grenades in barrels than scrolls and they actually scale.