Any faction that can get free points with summoning is going to be a problem eventually, and having each faction that can summon summon a different way is just going to lead to a year of loophole whack-a-mole. I can already think of several situations where Slaanesh's method of generating summoning resouces could be abused with just what we know now.
Also, the number of easy puns and lame double-entendres associated with Slaanesh are just two of a whole host of reasons why slaanesh is and always has been the worst part of warhammer.