When I first read your comment, I thought you were a little over the top, but it sounded like you likely had something solid to back it up, so I was interested in learning something new. Personally, I don't make strong statements like that unless I can pretty quickly defend them. I honestly wasn't trying to catch you out. And seeing a myth busted is generally a good time!
As for phone batteries, I just had to replace mine, so that's not a particularly useful example. As I understand it, there's a lot of circuitry in phone batteries these days anyway, so I'm not sure what failed. I'm not going to use my anecdotal evidence for or against your case, for what it's worth.
Be well!
I don't save a folder full of links to answer skeptical people on the internet and I'm not going to Google for you. If you're interested in reading articles, go look for yourself.
Anyway whatever. This has been a colossal waste of time.
Next time just say "sorry I don't have hard evidence for this opinion on hand". Nobody expects you to know everything but they do expect you to treat people decently.
I'm sure you have devices in your own life that disprove his claim. Look at your phone. Does it really go to 50% capacity after 500 days? None of mine have. Sure batteries degrade over time and you'll experience better performance one day or worse another, but he's claiming after 500 days of using your phone you should be at 50% capacity. That's obviously baloney.