I mean, it has a double jump and platforming sections. Sure it mixes genres, but I'm not sure why it's worth splitting hairs.
But the shooting elements of the game overtake the platforming
As I wrote, the platforming in R&C '16 makes up 1% of it, any more generous and I'd say 5%.
You do way more shooting than you do platforming
What about this is so hard to get? Megaman games are an example of an action platformer where the primary combat is using ranged weapons.
Just because you have (double) jump and a few platforming sections does not automatically make it a platformer; that has to be the primary core of the game.
That's like saying Uncharted series is a platformer because it has you navigating through ledges
Watch a playthrough of Super Mario 3D World, then go back and watch a playthrough of R&C '16 and tell me which one has the more platforming
I'm not saying the R&C series are not platformers BTW; merely that there is this bizarre misconception that R&C '16, this one particular game, is seen as a platformer, when after all is said and done it isn't.