The 600cc Super Sport class of motorcycles in world competition is highly competitive and involves a plethora of teams from around the glove. There are series in almost every western European country, the US, Australia and many countries in Asia as well as global race series such as World Superbike which has a Super Sport class for up and coming riders. Mind you, these motorcycles can achieve speeds upwards of 180 mph.
The more a manufacturer wins in these regional and global races series the more prestige they will obtain. Prestige is rewarded with buyers purchasing the stock versions of these race machines.
What is the incentive for a manufacturer to not make their engine better? Cost savings? If a particular manufacturer is continually winning on the track would another manufacturer not look for increases in performance for their next version of homologated 600cc performance motorcycle?
Currently manufacturers are adding various electronics for wheelie control, traction control, multiple fuel maps, next generation brakes as well as suspension. These are features are not trivial and cost real money and investment to develop and port to new models.
Having worked for Honda and a short stint at HRC I cannot see this kind of behavior working. The past shows us that the manufacturers will upgrade their motors in their stock showroom homologated vehicles in order to use those baseline engines in the super sport class so they can win.
They are spending millions flying eighteen wheeler trucks around the globe, hiring countless engineers for the race team, investing in the travel costs for the barrage of crew people necessary for the logistics, feeding and hotel costs for a single purpose, to win on Sunday. Why would they continue to do this under the guise of, we won't develop our brand and our technology further.
This stinks of urban legend. There is no logic in a gentleman's agreement and there is not citation I can find to back it up.
Honda, Kawasaki, Suzuki, Yamaha and others will continue to attempt to make the best bike possible in terms of performance and ride-ability because their reputation is tied into success. If they fail at winning their sales numbers will drop and that is NOT what a manufacturer is attempting to do. They are in business and have a profit motive as an innate feature of their existence.
There is no gentleman's agreement.