The problem is that there are several possible options for a lot of spells. Palsy could be Dispel Movement, Tap Movement, Summon Stasis, Combine Stasis Man, etc.
Another thing to think about from a game balance perspective is, what runes are more or less useful than others - until a rune has enough of a variety of spells for it to make it a worthwhile choice, it's dead end for a player to choose.
Has anyone made a spreadsheet of sorcery spell rune usage?