Intel has had Core i3,i5, and i7 lines for a decade, and when Ryzen was announced they had 3, 5, and 7, which was clearly meant for comparison against Intel. I

Intel has had Core i3,i5, and i7 lines for a decade, and when Ryzen was announced they had 3, 5, and 7, which was clearly meant for comparison against Intel. Intel created the i9 line shortly after Ryzen's launch, which you could reasonably claim was a natural progression. The introduction and numbering of Ryzen 9 was clearly a response to Intel having a tier that AMD didn't, the +2 happened not because it was the natural thing to do, it happened because that's what Intel did. If Intel had called i9 the i10, AMD definitely wouldn't have called their new tier Ryzen 9, they would have called it Ryzen 10.