I believe SS is pretty unbalanced if used in conjunction with Drizzle. I spent a lot of time using my SS+Drizzle team on the ladder and in tournaments to help get me familiar with the power of SS+Drizzle. And what I found was that SS+Drizzle pretty much has a certain win against some types and playstyles. Below i've listed scenarios that I have seen in my experience against specific types:
Normal - When playing against normal monotypes, usually the offensive pressure by SS teams is handled fairly well assuming the normal team is stall-styled. If not, it usually gets trampled without the help of chansey/blissey/snorlax/porygon2.
Fight - CC spam and a lot of priority is pretty decent against SS+Drizzle from what i've seen as access to sash breloom really does leave a dent in the SS-user's team. Nothing appreciates a spore followed by a bullet seed.
Flying - Flying is really fun to face. Access to Ludicolo/Kingdra spamming ice beams would make you think you have the advantage but bulky Zapdos can help with that as well as the top threat for SS teams, Mega Charizard Y. Drought + Solarbeam is really tricky to handle for SS users so you must be careful in preserving Politoed and predicting the right time to 'freeze' Mega Charizard Y in absorbing sunlight when it is going for Solarbeam by activating Drizzle with switching in Politoed.
Poison - Not so popular but really fun to see. With use of Tentacruel, it can tank some water moves. Access to Toxicroak with Dry Skin is also helpful and uses Drizzle to its own advantage as well. Mega Venusaur especially is amazing in stopping water in general. Greninja is probably the most effective to help in this scenario.
Ground - Ah, poor ground. Only hope is to preserve Hippowdon and Gastrodon for Storm Drain and Sandstorm. Drizzle+SS has access to Ludicolo as well as Greninja whom can both utilize Giga Drain and Grass Knot respectively. Ground usually does not survive against SS+Drizzle.
Rock - Rock is not very common though even if it preserves Tyranitar for Sandstorm, it usually does not help and still gets destroyed by SS+Drizzle. Cradily with Storm Drain is essential to survive (even then, Ludicolo can Focus Blast), or else Rock has very little chance of surviving.
Bug - Access to Sticky Web helps combat the speed boosts by SS as well as sash Galvantula with Thunder/Giga Drain leaving dents on the SS team. Although no walls on bug can really enjoy taking countless rain boosted Waterfalls and and Hydro Pumps which in turn falls down to the offensive pressure by SS.
Ghost - Some ghost types have access to grass moves though the ones that utilize this well are not bulky (exception of Jellicent). Will-O-Wisp is tricky sometimes too. I found SS is pretty dominant over ghost usually.
Steel - Access to Klefki and Ferrothorn is awesome as paralysis and a strong bulky grass type to tank water hits is very helpful. Steel is pretty neutral usually (situational though)
Fire - No chance to survive unless Mega Charizard Y/Ninetales is on the team. Same condition as with Flying. Drought makes it tricky.
Water - Ludicolo is great and pretty much dominates unless Suicune or something is setup already.
Grass - Ice Beam is great although Ferrothorn/Mega Venusaur/Cradily is hard to handle unless Greninja can pull through.
Electric - Pretty situational. SS tends to overpower despite the type disadvantage
Psychic - Neutral i'd say.
Ice - Freeze Dry is cool but still not enough. The offensive pressure by SS is too much from my experience. Avalugg is probably the only thing to tank physical hits which is obviously not enough
Dragon - If the SS+Drizzle user has Kingdra, you can pretty much outrage spam and repeat. Only thing to lookout for is Goodra to avoid the gooey speed drop. Other than that, it is a clean win usually.
Dark - Tyranitar is nice but can't survive too many water moves so it won't outlast Politoed most of the time. Not many walls can endure rain boosted Waterfalls/Hydro Pumps so eventually the pressure is too much for Dark and therefore falls to SS. Need to be cautious for Sucker Punches though, particularly from Bisharp.
Fairy - Need to watch out for Mega Mawile/Klefki but other than that, it gets eventually overwhelmed by the SS pressure
This has just been my experience with every type i've fought with Drizzle+SS and I am interested to see what other people say. Go mess around with SS+Drizzle and post here your experiences, replays and thoughts. I've given my Drizzle+SS team that I created for anyone to use
here
tl;dr
Summary: HO teams/some balanced teams and Ground monotype teams are severely effected by Drizzle+SS and are really at a disadvantage. If the opponent is not running stall, SS+Drizzle tends to dominate. If the combination of these abilities were to be banned, it'd be much more fair as the user would have to sacrifice a turn/moveslot to set rain up as well as not being able to switch in Politoed and activate Drizzle whenever they need it. This also allows for opponents to run other weather moves to counter rain if they wanted. That being said, i'd support a Drizzle+SS ban.