sorry about leaving, my laptop crashed and I had to go anyway (Plus I had lol like 10 pages open)
After thinking a bit more, I think your best plan of action is to add a fighting type to your team. Every team needs firepower and a fighting type will help you get past pesky walls like Blissey / Chansey. I think the best one for the job would be to use Breloom over Roserade. It's really standard, I know, but here are some benefits:
no more special wall weakness. Loom deals with Blobs well, and Tenta/Rachi can be killed by your two ground types.
keeps water resist- it's vital because a pokemon like Cloyster with Hydro P or Vaporeon can just sit and wiitle you down to low health.
it can set up- low and behold, a sweeper. Mach Punch can be used as ditch revenging, and Bullet Seed takes care of bulky waters, just like Roser.
Decent synergy with Tres. There's a flying weakness, but with Rachi and Chomp, it shouldn't be a problem
thanks for the team, man! I hope this helps