With single-sig, all your eggs are in one basket. Lose the key, lose everything. But multi-sig spreads things out so you need more than one key to unlock the funds. Even if one key is lost you can still recover access with the others (for example two-out-of-three signature setup). This gives you backups. Multi-sig wallets have clear benefits, especially for redundancy and security and you can't really compare them to single-sig wallets since they serve different purposes and give you varying levels of protection.
Storing your keys in more than one place under single-sig provides you with multiple backups.
Of course, having multiple backups for your keys in a single-sig setup will enable you that you can still access your assets even if one set of keys becomes lost for some reason. However, you still have a single point of failure. If any of these locations are compromised and your key is exposed (for example, stolen), your assets are lost. Therefore, multi-sig (or Shamir's secret sharing algorithm in the case of seed phrases).
That doesn't seem much different than having a single-sig setup with backups.
Not true. Read how the multi-sig wallet actually works because I don't think you fully understand.
I think for most a better and much more simple solution would be making use of passphrases/hidden wallets.
This has nothing to do with a multi-sig wallet setup.
Who said it did? Sure multi-sig may be a great option for you depending on your situation. I'm sure many institutions, companies and organizations make use of multi-sig.
But for the average individual joe, it is rather complex and difficult to manage, and there are more simple viable alternatives.
I disagree. We can argue that multi-sig wallets can indeed be seen as a bit more complex and require careful management, but, the added complexity comes with a higher level of security.
However, there are no "simpler viable alternatives" that offer the same, or at least nearly the same, level of security. This is evident from the simple fact that multi-sig wallets are preferred choice for those who prioritize safeguarding their assets, especially in business settings, when it comes to holding hundreds of thousands of bitcoins in cold wallets.
