When Rossi switched to Yamaha in 2003 or 2004, the whole point was to prove the “it’s not the bike, it’s the rider” philosophy. He got the shits with Honda because whenever he won it was the bike, they never gave him credit - he was expected to win because he was on the best bike. That’s why he left, then won first time out on the Yamaha in one of the best races ever against Biaggi at Welkom.
So it’s not the bike, it’s the rider proven? It seems so until you look at the wider picture and that is to say that he took his entire crew with him to Yamaha. Could he have done the same with a switch to Kawasaki or Suzuki?
If you look at F1, there are x many good engineers. The team with the best engineers makes the best car. Is it really Mercedes making the engine? Technically yes but really in this context “Mercedes” (or any company) is a team of engineers in a race shop making an engine with Mercedes cast into the cam boxes. The next year they could be working for BMW, Ferrari, Honda, whoever. Of course it wouldn’t happen like that but it could, because the engineers only represent that company for the duration of their contract. The same principal as any company/employee contract in fact, which is why it’s hard for me to understand why people do such cuntish things to fellow humans “for the good of the company”.
So I would say it’s not the bike, it’s the rider, the engineers, the tyres, the track and luck.
If I swapped bikes with Rossi, I took the M1 and he took my old 636 or my wife’s scooter (ok maybe not my wife’s scooter) he’d still kick my arse just about anywhere, and yours too!
So yes, in the right hands, generic RR sports bikes are competitive straight out of the box.
Also yes, the question is too open. I can see that it started as a drunken debate.