I totally agree with this! I think that clef sorta got tossed to the side in the beginning of Sun/Moon because we got so many good fairies, along with one dropping down from ubers. People sorta slept on it because some of the stuff that really dominated the meta either straight up destroyed it (Mega Metagross, Aegislash) Or ran options to hit it really hard (Sludge Wave Lando-I, Poison Jab Pheromosa, etc.) But the metagame has been really in its favor lately. Although its role has definitely changed between gens 6 and 7, and it may not be the S rank wonder that it was then, it's still a really great pokemon that's worth being ranked A.
The set I'll be talking about mainly is what is imo the best one, the max def bold set. I find it both the most splashable and the best to blanket check a number of things in the meta.
Clefable @ Leftovers
Ability: Magic Guard
EVs: 252 HP / 252 Def / 4 SpA
Bold Nature
IVs: 0 Atk
- Stealth Rock
- Moonblast
- Soft-Boiled
- Flamethrower/ Knock Off
That last set can be flamethrower or knock off. Both of them have a ton of utility - flamethrower is nice to get some really good damage on things like excadrill, skarm, ferro, celesteela, magearna and scizor that may want to switch in, while knock off is a lot better against stall. People often times leave in a chansey or a toxapex (Or an opposing clefable) and get their eviolite or leftovers knocked off. Obviously clefable is never going to 6-0 stall, but I've found that it definitely eases the match up. The utility of knock off is really nice against typical clef switch ins while flamethrower is pretty nice to hurt its common switch-ins.
Now to talk about clef itself in the larger picture of the whole meta. Clefable's role has changed a lot since gen 6 where it could effectively run a large number of sets like Calm Mind, SpDef, PhysDef, Rocks Clef, BoltBeam, etc. This generation, it really can't do every single role that it could in ORAS, but it still does its job effectively.
It does a nice job handling stuff like Garchomp, Mega Sableye, Mega Heracross (One of the few reliable counters to it), tangrowth, band zygarde (Unless iron tail then rip) and lots of defensive mons that it beats just because of magic guard being like a fantastic ability (Plus Mega Lopunny but I don't wanna talk too much on that cause it's not really been enough time to say anything about it) Pure fairy typing is so nice dude like you only got two weaknesses and a lot of resists, you get up rocks on oh so many pokemon while checking a bunch more. I find clef super splashable, and that it often brings a lot more advantages to the table than weaknesses. It doesn't necessitate a ton of team support - in fact, sort of the opposite as it provides rocks and checks to things like zygarde. It's nice to have a status absorber too, because it doesn't mind being burnt or poisoned.
To wrap things up cause I'm going super long and don't wanna get too repetitive, clef is a really good mon and deserves A. It handles a bunch of top tier threats in the meta, and provides soft checks to many others. Providing rocks, very nice bulk, and a good blanket check to another physical threat justifies a rise for clef imo. It may not be the meta defining beast in was in ORAS but it certainly is still a great pokemon to use.