That is one theory.And loss of reliability.
About 1 hp (+-) per 10cc of engine displacement is pretty close to the 'standard' for reliability.
310 GS = 32 hp or so. 390 KTM = 41 hp or so. FJR 1300 = 140 hp or so. etc etc.
On the other hand... professional 250cc Motocross with 48 hp = rebuild every race for factory teams.
GP bikes... 1000 cc engines.... 300 hp. They have 7 engines to get through a racing season.
Another is 1 BHP per cubic inch. This was first achieved in a mass produced engine ( disputably, but specifically promoted, and generally accepted to be ) with GM's 283 cu ins V8 with Rochester Ram-Jet fuel injection, matched with a manual transmission. Developed by Zora Arkus Duntov under GM's chief engineer Ed Cole, with help from John Dulza, the Ram Jet was launched as a $550 option ( in regular and high power versions ) on 1957 Chevys, including the 150, 210, Del Rey, Nomad, Bel Air, and Corvette models.
Given the comparatively light weight of these cars, they posed daunting potential racers. Campaigned under SEDCO ( which employed Smokey Yunick, and spawned the legenday Skunk works in 1958 ), the famous Black Widow 150 swept the field in 1957. So successful was the campaign that the NHRA banned fuel injected engines during that same season.
Wait, I've seen that car somewhere before.....