On Enamorus being completely budget Iron Valiant, you're underestimating how valuable a Ground immunity is to both teambuilding and switching Enamorus in:
252 Atk Great Tusk Ice Spinner vs. 0 HP / 4 Def Enamorus: 236-278 (81.6 - 96.1%) -- guaranteed 2HKO
You mispredict on pivoting Enamorus in, at least she survives stuff from Ground-types.
0 Atk Landorus-Therian Stone Edge vs. 0 HP / 4 Def Enamorus: 264-312 (91.3 - 107.9%) -- 50% chance to OHKO
This is the riskier Ground-type to switch into, but at least you can make Lando-T quake a little.
Which is why you don't lead with Samurott-H unless you really think the single layer of Spikes matters. And man have Spikes never felt weaker in OU right now. Samurott-H has a great defensive typing when it comes to partnering with Fairies or at least Enamorus, and I take advantage of that by having Samurott-H switch in on lured-in opportunities like Heatran, Slowking-G, Skeledirge, and Gholdengo. Unless Gholdengo is packing Focus Blast (or Thunderbolt) and getting the predict right, Samurott-H survives at least one hit from all of them and forces them out or blows them up (Heatran forces the Razor Shell). Unlike Greninja, Samurott-H gets actual strong priority and role compresses laying convenient entry hazards and forcing out Ghosts at the same time. I actually don't miss having a Stealth Rock setter when I have Samurott-H.
Let's see if it does so we can try Electric resists instead of immunities against Regieleki (note that Transistor uses the old multiplier and Electric Terrain simulates new Transistor):
252+ SpA Choice Specs Transistor Regieleki Thunderbolt vs. 0 HP / 4 SpD Baxcalibur: 170-201 (45.8 - 54.1%) -- 78.5% chance to 2HKO
252+ SpA Choice Specs Regieleki Thunderbolt vs. 0 HP / 4 SpD Baxcalibur in Electric Terrain: 148-174 (39.8 - 46.9%) -- guaranteed 3HKO
(252 Atk Choice Band Baxcalibur Ice Shard vs. 0 HP / 0 Def Regieleki: 186-219 (61.7 - 72.7%) -- guaranteed 2HKO)
Baxcalibur was a decent Regieleki check, but this is starting to get into switch-in-twice territory.
252+ SpA Choice Specs Transistor Regieleki Thunderbolt vs. 248 HP / 0 SpD Goodra-Hisui: 106-126 (29.2 - 34.7%) -- 38.8% chance to 3HKO
252+ SpA Choice Specs Regieleki Thunderbolt vs. 248 HP / 0 SpD Goodra-Hisui in Electric Terrain: 92-108 (25.3 - 29.7%) -- guaranteed 4HKO
OK, this one was terrible for Regieleki from the start. Goodra-H is even neutral to or resists all kinds of Tera Blasts to boot!
252+ SpA Choice Specs Transistor Regieleki Thunderbolt vs. 0 HP / 0 SpD Multiscale Dragonite: 151-178 (46.7 - 55.1%) -- 69.5% chance to 2HKO
252+ SpA Choice Specs Regieleki Thunderbolt vs. 0 HP / 0 SpD Multiscale Dragonite in Electric Terrain: 131-154 (40.5 - 47.6%) -- guaranteed 3HKO
Now consider Dragonite slipping out of OHKO range when Multiscale is chipped off.
252+ SpA Choice Specs Transistor Regieleki Thunderbolt vs. 0 HP / 4 SpD Roaring Moon: 149-176 (42.4 - 50.1%) -- 0.4% chance to 2HKO
252+ SpA Choice Specs Regieleki Thunderbolt vs. 0 HP / 4 SpD Roaring Moon in Electric Terrain: 129-153 (36.7 - 43.5%) -- guaranteed 3HKO
The Roaring Moon switch-in margins get more comfortable.
252+ SpA Choice Specs Transistor Regieleki Thunderbolt vs. 0 HP / 4 SpD Hydreigon: 165-194 (50.7 - 59.6%) -- 83.2% chance to 2HKO after Leftovers recovery
252+ SpA Choice Specs Regieleki Thunderbolt vs. 0 HP / 4 SpD Hydreigon in Electric Terrain: 142-168 (43.6 - 51.6%) -- guaranteed 3HKO after Leftovers recovery
(252 SpA Hydreigon Earth Power vs. 0 HP / 0 SpD Regieleki: 332-392 (110.2 - 130.2%) -- guaranteed OHKO)
Hydreigon can now switch in just that little bit more often.
252+ SpA Choice Specs Transistor Regieleki Thunderbolt vs. 112 HP / 0 SpD Kingambit: 346-408 (93.7 - 110.5%) -- 62.5% chance to OHKO
252+ SpA Choice Specs Regieleki Thunderbolt vs. 112 HP / 0 SpD Kingambit in Electric Terrain: 300-354 (81.3 - 95.9%) -- guaranteed 2HKO
(252+ Atk Supreme Overlord 4 allies fainted Kingambit Sucker Punch vs. 0 HP / 0 Def Regieleki: 313-370 (103.9 - 122.9%) -- guaranteed OHKO)
(252+ Atk Black Glasses Supreme Overlord 2 allies fainted Kingambit Sucker Punch vs. 0 HP / 0 Def Regieleki: 322-381 (106.9 - 126.5%) -- guaranteed OHKO)
I don't like needing 4 KOed allies to OHKO Regieleki with Sucker Punch without Black Glasses, but dodging the OHKO entirely exactly once with the new Transistor is clutch.
...It's definitely looking possible that the nerf to Transistor reduces the need to switch in a Ground-type into Regieleki just enough.
I still say keep Regieleki out of OU for at least the time being, especially since most of those mons are weak to Ice so they're a mispredict away from death, but this is excellent analysis and a sign that it's at least worth a (brief) look once things settle down.
---
What I'd ban: Magearna, and keep a very close eye on Chien-Pao. The rest of the 'broken' mons are exploiting the meta that Magearna creates (and Ursaluna exploits Magearna's ability to set Trick Room), and without that, might lose just enough to be manageable.
What I expect: Magearna, Chien-Pao, Zama-C, with a close eye kept on Zama-H and Ursaluna.