There is no need for any logic, just do the experiment for yourself everybody. Get two identical boats and removed the jib on one of them and see for yourself whether an ADDED jib is making you faster or holding you back.

When encountering a uni-rig believer, just ask him to place to largest possible mainsail on his boat and then go out and put a jib on there as well while keeping the mainsail and do again some on the water testing. He will huff and puff about maximally allowed sailarea and abruptly forget about any efficiency claims he made earlier. Of course you comply with his objections by fixing the maximally allowed sailarea to the total of the max size mainsail and jib combined. He will then only huff and puff indelligiaby and know he has been beaten.

Afterall, why does anybody have to agree to a such a low total sail area limit that it almost explicitly rules out the use of a jib ?

Nough said !

Wouter