Whilst I do not disagree with what you say, comparing the old v twin GP250s with modern day Moto Gp bikes is like comparing chalk from cheese.
The 250s were capable of 190-195mph down the straights, and with their lighter weight, accelerate faster out of the corners.
As Jap companies like Honda had to go and make 125,250 & 350 in 4,5 and 6 cylinders engines some revving to a Dizzy high 22,000 RPM :!:
for their GP bikes to complete against the rising two strokes in the 1960s, which eventually came to dominate the sport.
Even Yamaha made 125 and 250 V 4 water-cooled two stroke GP bikes in the 1960s mainly ridden by Bill Ivy and Phil Read.
The cost of making these exotic race machines proved too much for the Japanese factories, as they all quit GP racing around about the same time, leaving the door wide open for an Italian bike to win the world championship virtually unopposed for about the next ten years.
I hope I am proven wrong, but I can see the same thing happening again in MotoGP racing as the cost proves too much.
The FIM should have left the GP classes alone, but the powers that be assumed quite wrongly that a 4 cylinder four stroke with 16 or more valves to maintain, revving to 16,000 rpm, would be cheaper than a two stroke 250 twin cylinders, with two pistons with only one ring on each piston. ( Which was what this class was restricted to ).
How very naïve of them!
As for making the class slower, yes, that was the aim, as it happens in Formula One car racing nearly every year when they keep changing the rules to achieve this, to slow them down on lap speeds, as some of the circuits are deemed unsuitable ( by the ‘ealth & safely people :!: ) for this type of racing class.
http://images.search.conduit.com/ImageP ... rt=0&pos=1
http://www.mbike.com/honda/rc166-250/1966