While a weaker safe will not stop a thief who specifically targets the guns and brings the tools to get through any security (risking the extra noise and time), it can still prevent theft by an opportunistic burglar who enters looking for money or jewelry or anything valuable and easily stealable but finds an unsecured gun. It can also stop an opportunistic dishonest visitor who was invited in by a roommate (who may not know of his sticky fingers).
Locking something with low security locks will not stop all thieves, but will stop some (this applies generally, not specific to guns). So just because you cannot have the highest security does not mean that you should have no security.