Well the Western Roman Empire's army is in a much less shitty shape come the 5th century. Seriously, the two civil wars with Theodosius that the west lost were massive blows to western manpower. You know how Stilicho avoided battle almost religiously? Yeah, there's a reason for that beyond his questionable military capabilities: He couldn't afford any losses. This changes things.
Also, there's the Goths. The Gothic military capabilities are completely destroyed in this scenario. Theodosius used the Goths as a meat shield basically (something Alaric would not find amusing and would revolt afterward largely with that as his immediate justification). So in a scenario where he loses, the Goths are going to be completely crippled, and Alaric will likely be dead, meaning they'd be leaderless. Arbogast could likely use this as a means to secure far more favorable terms with them and set them up for being at least semi-assimilated within a generation (no state within a state with an independent ruler basically).