I liked Mazatlan--I was there a couple of times, but did not look into diving. From a quick search on SB, it looks like the question comes up every few years, but almost no one responds that they have actually dived in Mazatlan. In one thread, it was explained that the bottom is shallow for many miles out until it eventually drops off, and so the inshore dive sites, if any, get blown out easily. I found only a couple of instances where a SB'er replied they had actually dived in Mazatlan. One who is still an active member of SB is
@Darnold9999 . Looks like his trip was in 2007.