Ok, so let's talk about the pokemon posted in the OP
The Diggersby set in the OP is what I think will become the standard Diggersby, since it doesn't have the bulk to set-up anything tbh, especially not a Belly Drum (Although it DOES have access to that, so). There are 2 options that Diggersby can used over Stone Edge or U-Turn though. Explosion is one of them, doing massive damage thanks to STAB and Huge Power. To put into perspective how powerful Explosion from Diggersby is, have some calcs.
252+ Atk Choice Band Huge Power Diggersby Explosion vs. 252 HP / 0 Def Tyranitar: 364-429 (90.09 - 106.18%) -- 37.5% chance to OHKO
-1 252+ Atk Choice Band Huge Power Diggersby Explosion vs. 248 HP / 172 Def Landorus-T: 481-567 (126.24 - 148.81%) -- guaranteed OHKO
252+ Atk Choice Band Huge Power Diggersby Explosion vs. 252 HP / 252+ Def Hippowdon: 508-598 (120.95 - 142.38%) -- guaranteed OHKO
You get the idea. CB Explosion from Diggersby hurts like hell. The other option requires a different item, but I think that the Fake Out + ESpeed combo looks promising. Unlike other Fake Out users who can't really use it all that well, Diggerby's Fake Out is actually kind of strong, strong enough that Fake Out + ESpeed can take out threats that a CB ESpeed can, except without locking you in. It also lets you damage faster ESpeeders. These two moves probably don't have a slot on the main set outside of slashes (One kills you while the other one can't be used with CB, which is probably the best item for Diggersby). Countering Diggersby is really hard due to its ok bulk letting it live a single ESPeed from some ESpeeders while being strong enough to OHKO back. Sableye can't switch into a EQ, but otherwise works to a degree. Landorous-T kind of works as a counter, although it needs to watch out for Explosion. Drifblim and Gengar are immune to its STABs, but Stone Edge destroys them. However, he has to use Stone Edge on the switch, since both outspeed him. The best way to deal with Diggersby with CB is to predict, which is kind of an awkward situation to be in. For this reason, while not as strong, I feel that a Silk Scarf set is viable on Diggersby due to it powering up ESPeed and bluffing a choice set.
Sableye, imo, isn't as good as it was back in Gen 5, but that's because back in Gen 5 you could throw it at almost any set-up sweeper and destroy its life. While Sableye got a ton of new toys, it is also hurt by the introduction of Sylveon, Talonflame, Mega-Kangaskahn, and Mega-Absol (sort of). Syvleon destroys Sableye even if Sylveon is at -2 (-2 252+ SpA Sylveon Pixilate Boomburst vs. 252 HP / 252+ SpD Sableye: 273-322 (89.8 - 105.92%) -- 43.75% chance to OHKO), Talonflame has faster priority and can hit it hard at +2/+6 before Sableye can even Topsy-Turvy, and Sableye can't do much back if Talonflame hasn't set up unless its running Dark Void or Foul Play. Kangaskahn gives Sableye troubles, and while Mega-Kangaskahn can be beaten by Sableye, normal Kangaskan gives it trouble, especially since Will-O-Wisp isn't common on it anymore (Or I think it wont). Mega-Absol is only beaten by Sableye running Parting Shot, as it resists Foul Play and can bounce back Topsy-Turvy. However, it does check what it used to check a lot better, and what it checked way most E-Speeders, so overall I think Sableye is still a magnificent pokemon. I would run Max Defense over Max Special Defense though, since Will-o-Wisp isn't there to migrate his lower Defense unless you run it (but Sableye has HUGE 4MSS), and it helps you beat E-Espeeders due to being able to take their coverage moves better. The only thing I can think of that you lose to is Espeon, as Sylveon wrecks you even with max investment. Plus, Espeon can be dealt with by Parting Shot much like Absol. Sableye has huge 4MSS though, as it wants to run Will-o-Wisp / Topsy Turvy / Dark Void / Foul Play / Recover / Parting Shot / Destiny Bond / Taunt. This is why it's hard to say what the definitive "standard" Sableye is, but Topsy Turvy and Destiny Bond are definitely going to stay there as a staple to all the sets.
Sylveon is an amazing Pokemon thanks to Eevee and Pixilate Boomburst. Originally, I also thought that Earth Plate Judgement was the way to go for coverage, but honestly it's only needed for Heatran, as even resists get smashed by Pixilate Boomburst due to how powerful it is - only the bulkiest of resists can save themselves from a 2HKO. This means that Sylveon can run a mono-attacking set thanks to Fairy's good neutral coverage and the insane power of Pixilate Boomburst. I feel that, especially if you keep Judgement in the OPs set, Shadow Ball isn't doing much, as the only notable target you hit with it is Brongzong (Skarm gets destroyed by a +2 Boomburst - Specially Defensive barely lives). I feel that Lovely Kiss and Recover are much better options over Shadow Ball on that set, as one lets you cripple things while the other lets you gain your HP back. Extreme Speed requires a different nature, but it could work due to Pixilate boosting it to more than 80 BP and the +2 from Shell Smash could let it damage other E-Speeders. Baton Pass is also an option, allowing it to pass its Smash to something else and sweep later. Shell Smash isn't all it can run, it can also use a monoattacking set like I said. CM / Recover / Boomburst / Heal Bell or Lovely Kiss or Baton Pass can work very well. Another thing that Sylveon can do that everyone else seems to forget is Rapid Spin. Nothing is immune to Rapid Spin, so it's even better than Defog which could be blocked by Taunt. A defensive set of Boomburst / Softboiled / Rapid Spin / Heal Bell or Lovely Kiss could work well for it.
I don't see the appeal of Furfrou tbh. Yes, it has Recover now and Fur Coat is cool, but its main problem is still there - it doesn't do much. I feel that Rapid Spin is a waste of a moveslot on Furfrou since it is a Ghost magnet, as it cannot touch Ghost-types at all, plus other Spinners / Defog users do it better. Lovely Kiss is a much better option on Furfrou over Rapid Spin. Glare is also a neat option for Paralysis. Whirlwind should always be used over Roar imo unless something happened to Whirlwind that I don't know about. It's probably not the best thing in the world, but SD Furfrou could potentially work. It has decent bulk, recovery, and, most importantly, it can Baton Pass. Shell Smash with White Herb could work too, but SD seems like it can pass more than once per game. Overall, Furfrou could be cool, but I'm not seeing it as a great option.
Heatran is pretty good in the metagame. It can check Normal-types that don't have Ground / Fighting coverage due to Nature Power not being EQ this gen. I don't know how I feel about King's Shield. I can see the appeal to it, but I personally wouldn't run it. I'd much rather run Roar over it, but Kings Shield is neat and can work. Everything else on the set is pretty much what should be ran on the Specially Defensive set (I don't get the EV spread on the OP set though - is it trying to be defensive or offensive?). It is one of the best answer to non-BD Talonflame, if not the best, as non-BD Talonflame cannot do anything. Belly Drum gives it trouble however, as at +6 it 2HKOs while Heatran only does 25.34 - 30.08% to 248 HP EVs Talonflame with Searing Shot at 0 SpA. This might seem good for Heatran, until you realize that Roost + BD means that Talonflame wins that encounter. However, this does mean that BD Talonflame cannot set-up on Heatran unless it wants to take heavy damage. Sylveon needs Earth Plate Judgement to get around Heatran, however, it does this pretty easily (252+ SpA Earth Plate Sylveon Judgment (Ground) vs. 248 HP / 252+ SpD Heatran: 356-420 (92.46 - 109.09%) -- 50% chance to OHKO). Other Fairys do not get this advantage, and have troubles with Heatan. Azu needs to watch out for Kings Shield and Searing Shot burns, while Togekiss can barely 3HKO with Aura Sphere.
