Moreover I believe people play hanky-panky when talking about different geolocations of their backups, It’s easier said than done.
That's another possible use of multi-sig, though. If you truly have nowhere secure offsite where you can store a copy of a single sig seed phrase, then multi-sig allows you to compromise a little on that. I could set up a 3-of-5 multi-sig and store one back up with 5 friends, for example. Perhaps I don't trust any one of these friends enough to give them a single sig seed phrase, but I collectively trust them enough to know that 3 of them won't all try to betray me.
As pooya87 has said above, it's all about pros and cons, risks and benefits. Is the increased risk of theft offset by the decreased risk of accidental loss? Is the increased redundancy offset by the increased chance of discovery? It's up to the user to decide, but blanket statements like "Don't use multi-sig" are not helpful.
Having said that, in terms of your master seed proposal, I think it is less than ideal. Multi-sig is not just safer because it decentralizes your back ups; it is also safer because it decentralizes your seed creation process. If I have a device which is generating weak seed phrase (see the Libbitcoin Explorer vulnerability as an example), and I create a single sig wallet using it, my coins are lost. If I use it to create one seed phrase of a multi-sig set up with the other 2 (or 4, or whatever) seed phrases coming from a different device which is generating strong seed phrases, then I am protected from loss despite my weak seed phrase. If however I generate a master seed using that weak RNG, and then derive all my seed phrases for my multi-sig from this one weak seed, then again my coins are at risk of theft.
If you are going to generate a multi-sig from one source of entropy and store all your seed phrases as one single back up, then you've not really achieved anything at all. A single sig cold wallet would be a better choice.