252+ SpA Goodra Thunderbolt vs. 252 HP / 0 SpD Togekiss: 170-202 (45.4 - 54%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252+ SpA Goodra Draco Meteor vs. 252 HP / 0 SpD Hippowdon: 271-321 (64.5 - 76.4%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252+ SpA Goodra Thunderbolt vs. 252 HP / 0 SpD Politoed: 192-228 (50 - 59.3%) -- guaranteed 2HKO after Stealth Rock
252+ SpA Goodra Sludge Bomb vs. 252 HP / 0 SpD Clefable: 210-248 (53.2 - 62.9%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Goodra Draco Meteor vs. 0 HP / 4 SpD Terrakion: 226-267 (69.9 - 82.6%) -- guaranteed 2HKO after Stealth Rock
252+ SpA Goodra Draco Meteor vs. 252 HP / 0 SpD Latias: 332-392 (91.2 - 107.6%) -- guaranteed OHKO after Stealth Rock
You're pretty much never going to get the +1 boost against Mega Venusaur, and Assault Vest Goodra can spam attacks against it and stall it out of Synthesis PP.
The standard Rotom-Wash is physically defensive, and most Mega Venusaur are as well.
252+ SpA Goodra Draco Meteor vs. 252 HP / 0 SpD Rotom-W: 195-231 (64.1 - 75.9%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
-2 252+ SpA Goodra Draco Meteor vs. 252 HP / 0 SpD Rotom-W: 99-117 (32.5 - 38.4%) -- 97.8% chance to 3HKO after Stealth Rock and Leftovers recovery
(between the two, it is guaranteed, and Rotom-Wash can't touch you anyways outside of burning you, which special sets don't care about anyways)
So the only relevant KO that you miss out on with Goodra out of the ones you listed is the OHKO vs. Terrakion, which won't really be switching in anyways. Keep in mind that all of my calcs are from Assault Vest Goodra as well. You could be running Choice Specs if you want the extra power. Outside of luring a couple things, Choice Band Goodra is strictly inferior to special sets. You might be able to run some gimmicky physical set with Curse, but that's the only thing I can think of that wouldn't be outclassed by another Goodra set.
My bad about the Rotom, but still: 252+ Atk Choice Band Goodra Power Whip vs. 248 HP / 216+ Def Rotom-W: 254-300 (83.8 - 99%) -- 75% chance to OHKO after Stealth Rock
I'm not sure what any of these calcs show beyond choice band Goodra gets OHKOs that special Goodra can't. Even if you slap specs onto a special attacking Goodra, it fails to get the guaranteed OHKO on Togekiss, Politoed, Clefable, and Terrakion (and Latias without rocks). Some other stuff a banded Goodra can take on better than specs:
252+ Atk Choice Band Goodra Power Whip vs. 252 HP / 0 Def Tyranitar: 330-390 (81.6 - 96.5%) -- 62.5% chance to OHKO after Stealth Rock
252+ SpA Choice Specs Goodra Draco Meteor vs. 252 HP / 4 SpD Tyranitar in Sand: 207-244 (51.2 - 60.3%) -- guaranteed 2HKO
252+ SpA Choice Specs Goodra Draco Meteor vs. 252 HP / 4 SpD Assault Vest Tyranitar in Sand: 138-163 (34.1 - 40.3%) -- guaranteed 3HKO
252+ Atk Choice Band Goodra Earthquake vs. 252 HP / 0 Def Heatran: 568-672 (147.1 - 174%) -- guaranteed OHKO
252+ SpA Choice Specs Goodra Draco Meteor vs. 252 HP / 252+ SpD Heatran: 107-126 (27.7 - 32.6%) -- 76.1% chance to 4HKO after Leftovers recovery
252+ Atk Choice Band Goodra Outrage vs. 0 HP / 4 Def Conkeldurr: 280-330 (79.7 - 94%) -- 81.3% chance to OHKO after Stealth Rock and 1 layer of Spikes
252+ SpA Choice Specs Goodra Draco Meteor vs. 0 HP / 252 SpD Assault Vest Conkeldurr: 214-253 (60.9 - 72%) -- guaranteed 2HKO
252+ Atk Choice Band Goodra Outrage vs. 4 HP / 252 Def Blissey: 532-627 (81.5 - 96.1%) -- 56.3% chance to OHKO after Stealth Rock
252+ SpA Choice Specs Goodra Draco Meteor vs. 4 HP / 252+ SpD Blissey: 181-214 (27.7 - 32.8%) -- 80.8% chance to 4HKO after Leftovers recovery
252+ Atk Choice Band Goodra Power Whip vs. 252 HP / 0 Def Mega Blastoise: 306-362 (84.5 - 100%) -- 81.3% chance to OHKO after Stealth Rock
252+ SpA Choice Specs Goodra Draco Meteor vs. 252 HP / 4 SpD Mega Blastoise: 274-324 (75.6 - 89.5%) -- guaranteed 2HKO
252+ Atk Choice Band Goodra Iron Tail vs. 252 HP / 0 Def Sylveon: 424-500 (107.6 - 126.9%) -- guaranteed OHKO
252+ SpA Choice Specs Goodra Sludge Bomb vs. 252 HP / 252+ SpD Sylveon: 172-204 (43.6 - 51.7%) -- guaranteed 3HKO after Leftovers recovery
252+ Atk Choice Band Goodra Power Whip vs. 252 HP / 0 Def Jellicent: 480-566 (118.8 - 140%) -- guaranteed OHKO
252+ SpA Choice Specs Goodra Draco Meteor vs. 252 HP / 252+ SpD Jellicent: 217-256 (53.7 - 63.3%) -- guaranteed 2HKO after Leftovers recovery
252+ Atk Choice Band Goodra Outrage vs. 252 HP / 0 Def Goodra: 720-848 (187.5 - 220.8%) -- guaranteed OHKO
252+ SpA Choice Specs Goodra Draco Meteor vs. 252 HP / 4 SpD Assault Vest Goodra: 290-344 (75.5 - 89.5%) -- guaranteed 2HKO
I'm not saying banded Goodra would be crazy good or anything, but it's straight up wrong to say there's no relevant KO you get over special variants when using it. I'm comparing this to specs too, which isn't particularly common.
Also, what do you mean you're never going to get the +1 against Megasaur? Switch into a leech seed or Giga Drain and voila. The other guy won't lean away from using his grass type moves since few people run sap sipper, and even fewer run it with threatening physical moves to take advantage of.