Maus + Beat Up makes sense with both Archaludon and Annihilape, so the concept is not bad at all. Archaludon gets Stamina boosts from Beat Up, and Annihilape gets a powered-up Rage Fist. Then you also have the normal rain plan with Pelipper + Mega Swampert.
The main issue is that the team has almost too many win conditions and not enough glue. You have Archaludon mode, Annihilape mode, Swampert mode, and Mega Metagross mode all fighting for space. That can make the team feel strong when it works, but awkward when the opponent pressures you properly.
The biggest change I’d make is probably Metagross → Sinistcha.
Metagross is good, but it does not really fix the problems you mentioned. Sinistcha helps a lot more into Mega Swampert, Trick Room, and general pressure. It gives you Rage Powder, Hospitality healing, Matcha Gotcha, and your own Trick Room control.
I’d also change Archaludon to Body Press over Flash Cannon. If you are using Beat Up to boost Stamina, you want to actually turn those Defense boosts into damage. Otherwise Archaludon gets bulkier, but not threatening enough.
I’d change Pelipper to Wide Guard over Protect too. Wide Guard is huge for this kind of team because it blocks Rock Slide, Earthquake, Heat Wave, Make It Rain, Hyper Voice, Eruption, and other spread moves.
I’d also change Swampert’s Earthquake to Stomping Tantrum. Earthquake is awkward here because most of your team is grounded, so you end up forcing your own Pokémon to Protect. Stomping Tantrum is cleaner and easier to use.
The version I’d test is:
Maushold @ Chople Berry
Ability: Friend Guard
Level: 50
EVs: 32 HP / 2 Def / 32 Spe
Timid Nature
- Beat Up
- Follow Me
- Rain Dance
- Protect
Archaludon @ Leftovers
Ability: Stamina
Level: 50
EVs: 30 HP / 8 Def / 20 SpA / 8 SpD
Calm Nature
- Electro Shot
- Dragon Pulse
- Body Press
- Protect
Annihilape @ Sitrus Berry
Ability: Defiant
Level: 50
EVs: 28 HP / 22 Atk / 16 Spe
Adamant Nature
- Rage Fist
- Drain Punch
- Ice Punch
- Protect
Pelipper @ Focus Sash
Ability: Drizzle
Level: 50
EVs: 2 HP / 32 SpA / 32 Spe
Timid Nature
- Weather Ball
- Hurricane
- Tailwind
- Wide Guard
Swampert @ Swampertite
Ability: Torrent
Level: 50
EVs: 2 HP / 32 Atk / 32 Spe
Adamant Nature
- Wave Crash
- Stomping Tantrum
- Ice Punch
- Protect
Sinistcha @ Kasib Berry
Ability: Hospitality
Level: 50
EVs: 32 HP / 28 Def / 6 SpD
Relaxed Nature
- Matcha Gotcha
- Rage Powder
- Trick Room
- Protect
The team becomes much cleaner this way.
You still have Maushold + Archaludon as one mode.
You still have Maushold + Annihilape as another mode.
You still have Pelipper + Swampert as the rain mode.
But now Sinistcha gives the team a real defensive and anti-Trick Room piece.
The main thing is not to try to use every mode in every game. At team preview, pick the plan that looks best.
Use Maushold + Archaludon when Archaludon looks hard for them to break.
Use Maushold + Annihilape when Rage Fist looks strong.
Use Pelipper + Swampert when rain offense looks free.
Use Sinistcha when you need help into Trick Room, Mega Swampert, or heavy pressure.
Overall, I think the rain Beat Up idea is good. I just think the team needs less “extra attacker” energy and more support to make the main ideas actually work.