This is the same as people saying head movement isn't viable in MMA because of kicks and knees. Shitty head movement which sacrifices balance isn't viable (and some of the crazier, more showboatish style shit you'd see from the likes of Sweet Pea isn't viable). If you throw a shitty telegraphed jab to the body in boxing that sacrifices balance and position, your ass will get countered too. Not saying that De la Hoya was necessarily spot on, here, but the jab to the body is a legitimate weapon in MMA (and I've seen it used by many a Nak Muay to set stuff up and break fighter's rhythm).