Reference for what, exactly? There are no references that highlight the issue of storage performance in iPhones. I haven’t even found a review that looks at storage performance of iPhones in the past three generations. Brand new performance, not even performance over write cycle. That is the issue I’m raising.

If you want a reference that proves that NAND performance degrades over write cycles: then I will only list one, but there are hundreds, at least.

https://doi.org/10.1109/RELPHY.2008.4558857

Sure - entropy.

But is there any evidence that translates into an appreciable impact on device performance?

Perhaps it doesn’t, and this is why nobody is talking about it.