@DAMaz
I understand what Whitewing means. It`s all about balance. If the hero buy the Rune plate to armour their mage, then they`ve left someone else unarmoured. That should be the OL`s next target.
And about the conversion kit monsters, our OL looks at all the monsters he has and he usually ends up choosing the same ones, over and over, either because some are too easy to defeat, or don`t have abilities that generate enough win factor. Having a ton to choose from isn`t an advantage if they`re all mediocre choices for the campaign you`re playing.