There are a few changes to make to this team.
Firstly, I do agree with Asterat's suggestion of mixed venusaur. It is the set I use every time a build a sun team with venusaur, and it works.
Another thing is that your team is quite weak to dragons. Your only steel type cannot tank draco meteors at all, and most of those dragons carry a fire move anyway. The only suggestion I can give that might fix this would be mamoswine. Mamoswine packs a strong priority ice shard as well as acceptable bulk. It also carries one of the strongest earthquakes in the game. I really don't know what pokemon to replace it with; the best I can do is give you the set. I really am in no position to deem which pokemon to replace, as they have such good synergy that only you can know the weakest link.
Here is the set.
Mamoswine @Life Orb
EVs: 252 Atk, 252 Speed | Adamant | Thick Fat
Well, ice shard is great for killing the therians and dragons. Earthquake hits really hard. Icicle spear is secondary STAB for grass types. Superpower gets coverage on ferrothorn and other nasty stuff that walls mamoswine. Thick Fat removes its weakness to fire, although the moves are still stronger. It also gives it a nice resist to boltbeam, which is mostly fluff because that combination isn't seen much, but it is still very convenient.
Hope this helps!