I haven't seen it IRL. Macrumors postings tend to believe it's a mirror of the real world, but it's not.
I have seen a lot of iOS 16 devices, but that’s anecdotal.
I think that the interesting part is how, for example, the iOS 9 adoption rate by now was 77%. 72% now, which is a negligible difference, especially considering that the “earlier than the previous version” stat is at 4%, whereas before it was at 6%. Both are similar.
Interestingly, it seems that a lifelong history of device degradation through iOS updates has not translated into lower adoption rates. That has remained constant: us “oldest possible version holdouts” continue to be an extreme minority, in spite of lifelong issues (in terms of the entirety of iOS’ lifespan), with both performance and battery life.
Just my own baseless speculation, but I think this is due to five factors:
-Recency bias: people simply forget how good original iOS versions are, especially when they update through every single little point release ever. The decline isn’t sharp, such as the iPhone 6s: it did not go from 7 hours of LTE to 1 hour from one iOS version to the next. The decline is gradual, therefore, people forget.
-Acceptance: many have said “my device has terrible battery life and it isn’t fast, but it’s old, so it’s okay”. I obviously disagree, but I’ve seen that sentiment bounce around a lot.
-App support and features: the main updates candy. You can include security updates as another candy here, too.
-Larger batteries for iPhones: Recent iPhones’ battery life is infinitely better than it used to be. Severe decreases - in the realm of 40-50% - do not cause as many issues and they used to cause: if we have an iPhone 5s on iOS 7 or 8 with 6-7 hours of screen-on time with light use, and 4-5 hours of moderate LTE, a 40% decrease is enough to render it unusable. Grab an iPhone Xʀ, with 16 hours of light use, and 11-12 hours of moderate LTE, and a 40% decrease isn’t as significant. I reckon people consider maybe 10 hours of light use and 7 hours of moderate LTE enough so as not to be too bothered. Also, updated iPhones with larger batteries suffer less from degraded batteries than updated iPhones with small batteries, a significant factor.
-Performance improvements: In spite of severe battery life issues, performance after updating has seen a 180-degree change. The iPhone 4s is unusable on iOS 9, like others have said. The iPhone 6s on iOS 13 or 15 is pathetically slow when compared to mine on iOS 10, but it is certainly usable.
Let’s go to the middle: add 3 iOS versions to an iPhone 4s, iOS 8, and it is abhorrent. My 9.7-inch iPad Pro which was forcibly updated to iOS 12 is absolutely fine in terms of performance.
Regardless, with older iOS devices and older iOS versions being far more usable than they used to be, I am surprised that it hasn’t evolved at all.