People mock Excel's encryption, mostly based on the outdated binary format's "encryption" (which admittedly was a joke). Modern Excel is actually legitimately secure, it uses PBKDF2 (5K rounds) to hash the user's password then AES-256 for the actual encryption.

So while Bitwarden is more secure than modern Excel out of the box, neither one is a slouch. You'll definitely spend a lot of compute cracking either one. The weakest part, as always, is the user's password.