Did you just started playing the game? You should of seen when there wasn't any dispel shields. Players were able to spam dispels especially around tournament time. As for the answer to your question Dispel prevents the opponent or mob of which the spell was cast upon for said schools of nature to fizzle and lose pips or shadow pips. Its not a cheat this has also been this way since the beginning of the game. Its a way to prevent the caster of the opposite spectrum to cast the same spell if that spell required a x amount of pips. Therefore it doesn't really affect if you cast a shield weakness or blade you are still able to keep the pips.