If Rossi wasn't faster than Vinales, he never would've caught up to him to be able to slipstream him on the straight! That's the point. You're acting like Rossi only got pole because he was in Vinales' slipstream getting towed around the lap. He didn't catch Vinales in acceleration zones because of a tow, he closed the distance in all the braking zones. The slipstream on the straight to get under the last bit of time to get pole was the payoff for excellent riding earlier in the lap.
Correct MV but without that draft on the straight the chances of him getting pole are reduced and I suspect that this is what has irritated Suzuki if the story is accurate and/or correct, as after all it would have been their first team pole for many years.
Personally, I have no real issue with drafting although I do understand the issues that many do, but my take is that as it is legal in the race thence I fully expect people to draft in practice even if it is a frowned on activity. Sure some people will gain an advantage by jumping grid spots and what not but really, if the rider cannot maintain the pace they will not stay in the position anyway come race day