I'm skeptical of that theory because I don't see any of the sloops furling their jibs when going upwind. There has to be some marginal payoff to having a jib when going upwind. I do agree that you'd be better off having that jib area in your main instead, though.

I've also heard many sloop skippers claim that they can't point well unless the jib is sheeted in hard. Maybe that's because they steer to the jib telltales, while it'd be more profitable to let the jib out and let it luff a bit. I guess I'll have to experiment with that.