Heck, if all they sold was a Macbook Pro from 2015, quite a few developers would be happier about it.
They can open source or license OS X. Not within their current strategy, but that has to be one of their backup plans.
That said, slower sales doesn’t mean less users, because replacement times are just getting longer. I’m using a late 2016 MBP, and Apple isn’t expected to have a meaningfully better one until late 2022 or so.
Even the iPhones have really only changed cosmetically since the 6S came out three years ago. This year’s model will be the first one since then that will actually be noticeably faster.
According to this link, the currently shipping iPhone is roughly 1.75x as fast as the 6S (Geekbench score of ~4200 vs. 2400):
Latency is an issue, sure but not as much as CPU here.
Until they release a 15" non-touchbar version with a better keyboard, I'll stick to my 2012 rMBP, as I'm sure others (including people I know) are too.
If you've got a Core i series CPU, your laptop will age fairly well and potentially delay your upgrade. Maybe that's the cause of the decline?
Good on Apple marketing though, it stuck hard and each time someone makes a cute comment like OP's, it's just free advertising for Apple.