At some stage coincidences have to start adding up and unless you're a mindless sheep you should say well maybe there's something going on here.
Let's consider this.
2013 - Rossi returns to Yamaha and runs a distant 4th gets lucky win due to Lorenzo being injured, Pedrosa being Pedrosa and Marquez being inexperienced.
2014 - Rossi runs a distant second beating Lornezo and Pedrosa both of him prefer softer tyres than Rossi. Marquez who like Rossi prefers harder tyres with stiffer carcass' but rides them better goes on to have 13 races wins and crashes out of the lead twice. Rossi has a much better season, much more consistent and scores a heap of points. Is it not out of the realm of possibility that Maruqez incredible run in 2014 and End of career resurgence could've been helped greatly by tyres that were more to their preference?
2015 - Marquez refuses to settle for any positions a bad bike and stupidity on his own part eliminates him from the race. Rossi gets a strong start to the season but Lorenzo starts to find form with a new tyre and wins 4 straight. Tyre is then weirdly withdrawn for Assen, Marquez excaims we all know why but we are not allowed to say. Rossi chokes down the stretch, Lorenzo wins, Rossi finds someone else to blame.
2016 - testing is dominated by Lorenzo, front tyre that he used to dominate on is withdrawn on safety concerns after rear tyre problems. It becomes a 2 horse race for the title between Marquez and Rossi who both prefer harder tyres as Lorenzo and Pedrosa in particular struggle to get feeling from the harder front tyres. Heavy brakers like Rossi and Marquez do well.
Not one of these things that happen point to anything untoward taking place, but all of those coincidences, all these strange things happening that all seem to help Rossi. It has to at some point be by design. There just seems to be too many small things that happen that end up helping Rossi and/or hindering his competition tyre wise to just simply be a coincidence. The issue is that if you give Rossi his favoured tyres Marquez will ride them better and run away with a championship how he has done twice, once with an unfavourable bike.
2017 could provide even more coincidences. None of these coincidences ever seem to hurt Rossi, while things have happened to hurt all of his rivals since '07.