Hey invalio, you seem to have the right idea with this rain team but I think there are a few things that could really help your team out.
First of all, I would switch metagross to mamoswine
. Mamoswine still has acces to stealth rocks and has stronger ice and ground attacks than metagross. Plus it's priority helps you against dragons and it forms a great offensive core with breloom.
Secondly, I would change latias to latios
simply because it can hit much harder and you say you're looking to muscle past walls so that change would definitely help there. You could run the exact same set no problem.
Some move changes you may want to consider are low sweep over swords dance on breloom, Giga drain or fiery dance over fire blast on Volcarona, and recover over ice beam on starmie. However these would all be pretty minor changes and it's really personal preference what you run.
I think your team is really solid now since mamoswine deals with all of the threats you mentioned bar terrakion but he can be easily revenge killed be breloom's Mach punch so he really isn't too much of a problem. If it remains a problem though you could switch your scarf to latios and make politoed choice specs.
Anyways hope I helped and good luck with the team! Here is the mamoswine set