The 7 had real new features such as water resistance (a very big deal at the time), the A10 Fusion chip which was a huge improvement over the A9, stereo speakers, a much better camera (and was the first to include more than 1 camera lens on the plus), a new home button and somewhat different design on the rear and increased base storage for the first time since 2010
The 6S was pretty much exactly the same as the 6, apart from RAM which nobody cares about. I kind of get the impression that some people still haven’t got over the removal of the headphone jack and for that reason glorify the 6S and downplay how much of an upgrade the 7 was over it. Meanwhile the 6 was absolutely groundbreaking and one of the most memorable and large upgrades, up there with the original, the 4 and the X
The fact they were both dropped at the same time means nothing. I actually think Apple should have shown more courage and dropped all pre A12 iPhones for ios16