Yeah I agree the VR needs some serious revamping, but it's definitely salvageable so don't sweat it.
Toxicroak is definitely not a high tier rain sweeper. Yes it works very well on rain and can help deal with many of rain's checks such as Mega Venu, bulky Waters, Ferro, and Keldeo, but it's just so hard to fit it on a rain team that I really can't see it being compared to rain staples such as Kingdra, Ferro, and Torn-T. It can work well under the right circumstances, but it's not something you can afford to just slap on most rain teams and call it a day. It's definitely a perfect mid tier Pokemon on rain, as it can be very effective with the right support but it just can't find its way on rain teams like most of the Pokemon found in Top level.
I agree that Mega Hera or Mega Pinsir could probably move to top, but prerrably Mega Hera in my opinion, as it not only breaks most of what Mega Pinsir is designed to beat on rain such as Mega Venu, Ferro, Celebi, and Bisharp. It's slower and lacks priority like Pinsir, but Mega Hera's main purpose on rain is to beat what rain struggles with, and it really doesn't need much support at all to accomplish this. Mega Pinsir still does a great job at picking those mons apart, but tbh Mega Pinsir on its own needs a decent amount of support to be very effective, as SR severely hinders how often it can come in and mindlessly spam Return, and while Defog isn't uncommon on rain, Mega Pinsir can often force you to play a LOT more aggressively to keep SR off the field, as most rain teams wont have too many opportunities to bring something like Latios in to Defog. Mega Hera is by no means immune to hazards, but Mega Hera just seems to fulfill its job as a rain wallbreaker more effectively than Pinsir, without needing as much support, which is why I think Mega Hera should be top tier while Mega Pinsir feels like it fits better in mid tier. The fact that a healthy Mega Hera can also take on Thundy, Raikou, and Mega Mane (with rain up), 3 huge threats to rain, is huge for it as well.
Quag, Roserade, Forry, and Chansey just don't seem solid enough at all on rain to ever be used as much as something like Mega Pinsir or Omastar lol. Defensive rain is pretty bad considering you're much better off just taking advantage of how many good offensive abusers of rain there are, and how most of the defensive Pokemon found on rain can easily be taken advantage of and rely on rain, which only lasts for 8 turns. The reason why offensive rain teams are so effective is because in just those 8 turns, Pokemon such as Kingdra, Torn-T, and Kabutops are able to deal so damage considering that not much in the tier is able to handle rain boosted Hydro's and Waterfalls or Hurricane spam coming from Pokemon that outspeed most of the metagame. A key strategy in playing rain very successfully is trying to keep up the momentum as much as possible in order to fully benefit from the few turns of rain, which is easy to do with a faster paced team, but with slower, more passive threats, your momentum is going to be killed a LOT, thus not taking full advantage of rain's benefits. On defensive teams, most of the time you're going to be switching quite a bit, as well as spamming recovery moves or occasionally setting up hazards. Tent is a mediocre spinner even IN rain, and outside of rain it's worn down very easily. Roserade is mostly outclassed by Amoonguss defensively, and offensively you're better off using Mega Venu as it is MUCH bulkier and still hits plenty hard. Forretress is just COMPLETE ass as a hazard remover because it loses to literally every spin blocker in the tier and is just complete Mega Sableye food, so up against any Mega Sableye team you're NEVER going to get up hazards or spin. Chansey is just extremely niche to very defensive teams, and I can't see Chansey wanting to be put onto a rain team considering it just makes it even more Manaphy bait, especially if you lack Goth.
Also fuck no leave Carracosta unranked. It's almost completely outclassed as a Smasher by Omastar, and physically Kabutops is just far superior. Being outsped by practically every relevant Scarfer REALLY sucks too. I can't see it being useful as anything else, it sounds pretty horrible defensively too.
tl;dr
Toxicroak > Mid Level
Mega Hera > Top Level
Drop Quag, Rosy, Forretress, and Chansey completely
