If pure performance is what you want, that is probably true.
The more fuel/air you can ram into an engine, the more power you will get.
If you look at the difference in performance on the old British bikes that had twin carb and single carb options, the single carb bike would typically make 85-90% of the peak power, torque dropping behind at high rpm.
Flexibility and traction at low revs was generally better, and the big bonus was fuel economy.
Single carb 650's would generally return 55-60 mpg, twin carbs 40-45.
That's on imperial gallons BTW.
In affluent 1960's America, with gas at $0.25 a gallon, that didn't really bother anyone.
Buyers wanted maximum performance, the cost of the extra fuel was irrelevant.
Unfortunately for us, Yamaha never considered a single carb option, or they wouldn't have designed the frame with that vertical tube so close to the head.
It would be interesting to see what an XS engine would do, suitability equipped with an equal length manifold and a good CV type carb, like the SU conversion for the Norton Commando.
Unfortunately you would need a special frame to achieve that.
