Sand is not going to become omnipresent and frankly put, that does not make clefable anywhere close to being B. Clefable can still check ttar despite sand cutting into its healing, since it doesn't like taking knock off or moonblast, and any non stone edge move tickles it. The bulk has never been amazing, but thats not the point of it, its a defensive pokemon that does not care at all about passive damage, which is such an amazing thing. A lot of tyranitars are also dropping smooth rock, which means moonlights recovery reduction is less of an issue since its 5 turns max, which like, isn't the hardest thing to outstall. Clefable is A/A- minimum, anything below that (or even to B rank), is simply put ridiculous. It has a ton of other good mus (ting lu, zama, tusk, dragapult, garg etc) that make it an elite pokemon.