Splitting your seed phrases into two locations is necessary because if a natural disaster like earthquakes, floods etc or an accident like fire happens in one of the locations where you stored your seed phrases, you can be able to recover it in the other location but multisig account is just for you and a third party to own custody of your wallet and not because of security reasons. However, the idea is not flawed if you don't keep them in a location where it can be seen by others.