It's not that non-yamaha parts aren't genuine. When someone recommends using genuine yamaha jets they know when you install it that it "shouldn't" blow up your engine or cause a rough running bike because the parts have been proven in the field already by that forum member. The flow rating of non-yamaha jets are not as well tested by the forum member offering the advice. They are protecting you.
Dynojet gives their "genuine" jets a number. For example, 130. Yamaha gives their "genuine" jets a number, example 130. BUT, the numbers are just arbitrary and doesn't mean they actually flow close to the same amount of fuel, despite having the same number. You install 130 Dynojet and we meant 130 Yamaha and then your engine goes BOOM and you get mad.
You're looking at it wrong, in my opinion. Lots of genuine parts out there.
I'm running a "genuine" non-yamaha jet.