I was considering the aspect of the trust to developer(s)/team(s) that have responsibility for wallet. Multisig would help to safe my funds if the security design pertaining to particular wallet were failed somehow.
If your wallet software failed to generate properly a multi-sig wallet, what makes you think that it won't happen to a single-sig too? I'm not sure that I'm following you.
Well, let me consider the hypothetical situation when one of the wallet has backdoor that give the adversary chance to steel my fund. The latter may happen if this wallet is kind of single-sig one but would never happen if it's multi-sig (say 2-of-2) wallet because in this case it were required the second private key to sign transaction.