Single sig with a strong passphrase could be constructed to be like a 2-of-2 without a passphrase, secrecy speaking.
That’s the simple take. There are many other considerations for 2-of-2 to take into account, like opsec, evil maids, etc.
Discussion
So for arguments sake, hypothetically, if you had a 2 of 2 and one seed was compromised, would your ₿ stack be more in danger than if you just had a single sig setup?
Also if you had a single sig w/ passphrase and your passphrase was compromised, would that impact the security of your ₿ stack?
All things equal and no other risks taken into account in the hypothetical, no.