Nakajima was also very good.
Rossi was the only one of the Yamaha riders that said the development direction and updates were wrong and ineffective all the way back at Valencia 2016. Zarco and MV (after a lot of kilometers, time and testing) all came to agree with him. I recall Zarco dismissively saying that the 2017 M1 had a better chassis than the 2016 M1 concept...then on the last day of winter testing, concluding that Rossi was actually right.
I agree that it's possible, but the intuitive conclusion is that his development skills would've only improved after having raced every bike and tyre configuration under the sun.
It is also possible his riding repertoire has become limited and doesn't suit the tires or whatever.
I do think the current Ducati is just a straight out faster bike though. The Honda seems fairly MM dependent. I couldn't see even him beating the current Ducatis on a current Yamaha though.