In Gen V, Drizzle+SS was banned for the combination of speed and power it gave Kingdra, Kabutops, etc. The main reason for the ban was because Drizzle boosts Water-type STAB in addition to the Speed of Swift Swimmers. With Gen VI coming around, Drizzle is no longer permanent, so you can basically stall out the Rain and the Swift Swimmers can't sweep. So, in OU, the combination of Drizzle+SS was unbanned.
However, in Monotype, for certain types, there is no such thing as stalling out Drizzle. You can't just slap Ferrothorn, Mega Venusaur, or Chansey on any team you want. Mono-Fire auto-loses to mono-Water no matter what, as neither Charizard nor Ninetales can touch Politoed. Mono-Normal's only answer to mono-Water is Chansey, which is shaky at best thanks to Kabutops. Mono-Electric has nothing to take on a Jolly Kabutops in Rain other than Scarf Jolteon, Scarf Electrode, and random Sashed mons. No member of a mono-Dragon team (with the exceptions of Latias and Goodra) can take Ice Beams, or Kingdra's Dragon STAB. Mono-Flying flat out loses to Kabutops thanks to its lack of priority users (and no, Talonflame would not have helped) and mixed walls. Jolly Kabutops even outruns Timid Scarf Thundurus-I. Mono-Bug's best answer is defensive Mega Scizor, which has to be 2HKOed by either Kingdra or Kabutops depending on its EVs (and is 2HKOed after Rocks regardless). Mono-Ghost, mono-Dark, and mono-Psychic are pretty screwed too, with mono-Ghost relying on Aegislash and mono-Psychic on AV Metagross, neither of which can take down more than 1 Swift Swimmer in any given game. The only types that can consistently beat Water are Steel, Grass, and Poison, the former two because of Ferrothorn and the latter two because of Mega Venusaur.
On the other hand, the above scenarios are assuming the mono-Water team gets Drizzle up, and then gets their sweeper in reasonably safely so that it can then proceed to wreak havoc. We all know that's a lot harder than it sounds. But is it really that difficult? Keep in mind, that if the opposing team has no way to deal with it, it only needs to enter the game and take less than 50%, so it can survive six rounds of LO recoil. Neither Kingdra nor Kabutops can be considered "super frail". If the Water user times his Politoed switch-in correctly, Kingdra or Kabutops can easily get a switch-in on a foe that can't damage it much, for example, Charizard (which Politoed completely screws upon switching in). Also, mono-Water has a lot more mons than just Politoed, Kingdra, and Kabutops. It has a scary amount of Shell Smashers, such as Omastar and Gorebyss. It's also got Mega Gyarados, another opportunity to sweep. Gorebyss can also SmashPass, which basically eliminates the need to set up Drizzle before Kingdra or Kabutops plows through everything. Or, pass the Shell Smash to Keldeo. Good game.
I do believe Swift Swimmers need some sort of nerf, whether it be a Drizzle+SS ban or Damp Rock+SS ban. But on the subject of a Damp Rock+SS ban, would it really be enough? Normal Drizzle gives the Swift Swimmer 3 turns to wreck shit. In any given game while playing Talonflame, that's the number of turns you expected Talonflame to last before dying to recoil (unless of course you ran the Stallbreaker set). The fact that a few monotypes have less checks to Swift Swimmers than Bug had to Talonflame doesn't really help here. The difference between Swift Swim and Talonflame is that Swift Swim requires a lot more preparation, but is more powerful.
First off I believe swift swim needs a nerf, so I will make my position on this issue clear. A mechanic that basically doubles the speed and adds a choice band/specs to water pokemon is pretty overkill for teams not carrying a different weather inducer, mega venu, or normal cores. With the option to add Keldeo with a CM sub set onto water teams then even Normal teams will start to struggle against Swift Swim water.
That being said the examples AOPSUser brought up have glaring errors. Mono Fire does have a bad time against Swift Swim but its not an auto loss, usually the match gets decided on which pokes each side starts with. If the fire user starts with Chari - Y and the water user starts with Politoed, then the water user has to switch because when Chari goes Mega, Drought is reapplied, combined with Solar beam which ever poke the water user switches to will take a big hit. Afterwards its a matter of prediction, its not hopeless good fire users have won against Swift Swim users (admittedly Talonflame does play a significant part in this). If the Swift Swim team does not have a stall breaker like Keldeo, or to an extent Mega Gyara, free switching between Chansey and Pory2 will safely stall out the rain and also give the ability to inflict status such as paralysis from Thunder Wave onto the Swift Swim pokemon, making them a lot more manageable. Here are calcs so you can have an easier time understanding, based on 3 prominent pokemon on swift swim teams, Kabutops, Kingdra and Ludicolo
252+ SpA Choice Specs Kingdra Surf vs. 252 HP / 252+ SpD Eviolite Chansey in Rain: 136-162 (19.3 - 23%)/252+ SpA Choice Specs Kingdra Surf vs. 252 HP / 4 SpD Eviolite Chansey in Rain: 187-222 (26.5 - 31.5%)
252+ SpA Life Orb Ludicolo Surf vs. 252 HP / 252+ SpD Eviolite Chansey in Rain: 114-136 (16.1 - 19.3%)/252+ SpA Life Orb Ludicolo Surf vs. 252 HP / 4 SpD Eviolite Chansey in Rain: 157-187 (22.3 - 26.5%)
252+ Atk Life Orb Kabutops Waterfall vs. 252 HP / 252+ Def Eviolite Porygon2 in Rain: 133-157 (35.5 - 41.9%)
Now lets move on to Electric, they do have pokemon that can force Kabutops to switch Magnezone just needs full HP investment to comfortably eat a Rain and Life Orb boosted Waterfall in the rain and KO back with thunderbolt, Rotom-Wash can do so as well. If the water user carries Lanturn however then its a different story, as Lanturn safely walls most SpA oriented electric pokemon barring Mega Ampharos due to Mold Breaker even then Lanturn still has enough Bulk to withstand multiple dragon pulses/discharges to confuse ray back or inflict lucky burns via scald. Here again are calcs to back up my points
252+ Atk Life Orb Kabutops Waterfall vs. 252 HP / 0 Def Magnezone in Rain: 230-270 (66.8 - 78.4%)/252+ Atk Life Orb Kabutops Stone Edge vs. 252 HP / 0 Def Rotom-W: 203-239 (66.7 - 78.6%)
252+ SpA Mold Breaker Mega Ampharos Dragon Pulse vs. 252 HP / 252+ SpD Lanturn: 156-184 (34.3 - 40.5%) / 252+ SpA Mold Breaker Mega Ampharos Thunderbolt vs. 252 HP / 252+ SpD Lanturn: 166-196 (36.5 - 43.1%)
As for Dragon teams, I do not have enough experience on this matter, but I think you are right that Swift Swim is hard to dragon types to overcome. I will try to get Soma to comment on this since he has some success on the ladder and he has faced Swift Swim teams.
Im not entirely convinced Flying is at a complete loss as you've suggested first off no one in their right mind would send in a Thundurus in on a Kabutops, not when Skarmory can wall it so safely even in the rain. Thundurus is much more better served as a late game sweeper or as a utility pokemon to prankster thunder wave a threat.
Bug teams actually have a decent time vs Swift Swim. Once Sticky Web is setup, a scarved Heracross instantly becomes a threat with moxie close combats threatening to sweep the team. Once enough debuffs are wracked up Hera can simply switch out and repeat the process after the fodder dies. Positioning is key here in that Kabu must be available to spin away that hazard if needed.
Ghost struggles, im not even going to try here, I can be wrong and if so someone post the reasons and the why so Ghost users can know what to do.
Dark has a decent chance unless facing Sub CM Keldeo, the water user has numerous opportunities to send in Keldeo and setup a sub against a dark team, once this happens its hard for the Dark user to get out of that situation.
Psychic actually has a pretty easy time countering Swift Swim, choice gardevoir with trace and thunderbolt/moonblast works wonders.
Steel will face trouble against a Swift Swim user with a keldeo on their team. After softening up Ferrothorn with Ludicolo, Keldeo can then come in and finish it secret sword. Of course nothing is this easy but keeping in mind while the pokemon are switching around eating Rain boosted stab water attacks will take a toll on the Steel team.
Grass/Poison finally does have it easy. Mega Venu is a hard counter and it is an obstacle for swift swim teams to overcome.
On the subject of baton passing shell smash with swift swim pokemon, that is very unlikely to succeed unless you opponent is off their game no player should give the water user the turns needed to first switch into huntail/gorebyss then allow them to do a shell smash and then baton pass it to a pokemon. Im sorry but with the limited turns on Rain, it is not needed and frankly a waste of a turn. Rain boosted water attacks are usually enough to land KOs especially with Life Orb/Specs/Band boost on most pokes that aren't ev'ed to tank hits. And the pokes that do tank hits usually have some sort of utility move to cripple the threat like thunder wave.
In the future AOPSUser I would hope you take effort to test out your opinions before you post them. Your brand of theorymonning doesn't help the tier and in fact perpetuates ignorance.
But you are correct that Swift Swim needs a nerf/ban though. Swift Swim by itself is counterable, but with the huge pool of pokes a water user can draw upon, they can get pokemon to cover the weaknesses in the team Keldeo and Lanturn being good examples.