I see where you're getting here, but even with just 4 bikes, he still beat 2 of them during the last 3 years, that's something you can't ignore, and definitely not 'uncompettive'. Le Mans has proven that with a well setup bike, Rossi can match Vinales' ridiculous speed, and while he screwed up badly, was still pretty competitive to me.
I agree that if Zarco were to hop on the M1 that he might actually do a better job than Rossi, but sadly Yamaha already has a ridiculously fast rider (Vinales) and with a legendary name such as Rossi, with the amount of fans he has, and the amount of people that want him to get the 10th title, the PR he generates is something a manufacturer would be foolish to just throw away. Thats the game of MotoGP now. Does Zarvo or anyone else deserve the M1 seat? I'd say no, only because Rossi didn't get to where he is by chance, he earnt it. He's 38 and taking on people over a decade younger than he... I'd watch that, and so would others.