anyone else keeping files on two clouds just in case onedrive goes down?

You've perfectly described the "cloud sprawl" that happens naturally—work dictates one ecosystem, clients another, and personal history (like old Dropbox projects) adds a third.

The anxiety you felt when OneDrive silently stopped syncing is the exact reason why the "3-2-1 backup rule" (three copies, two media types, one offsite) is still the gold standard, even in a cloud-first world. Relying on any single cloud provider is effectively trusting their infrastructure, their software updates, and your own network connectivity all at once.

Your setup with All Cloud Hub solves the operational headache of managing that sprawl, but as you noted, it doesn't replace the need for a true backup strategy. 

Potential Gaps to Consider…

Sync is not Backup: If a file gets corrupted, encrypted by ransomware, or accidentally deleted and that change syncs across all three clouds (via a tool that bridges them), you lose your redundancy. A true backup is versioned, immutable, and air-gapped from your active sync environment.

Tool Dependency: While All Cloud Hub uses OAuth (which is secure), you are introducing a fourth-party tool that has API access to move files between your clouds. It’s worth verifying their data handling policy regarding file metadata and transfer paths to ensure files never touch their infrastructure (most reputable aggregators use server-side transfers directly between cloud APIs).

Since you mentioned using All Cloud Hub, it’s worth noting that for users who prefer open-source or offline tools, Rclone (command line) or KDE Plasma's "KIO GDrive" (for Linux) offer similar aggregation capabilities without a web-based middleman. However, for a clean dashboard UI, the tool you’re using fits the "three tabs to one dashboard" requirement perfectly.