I think the supply chain is pretty broken. I had just about the same experience as you with an iPhone 7 a few years back. I booked my replacement through Apple's website, so I was pretty confident I wouldn't get scammed. The new battery started bulging in less than two years, to the point that there was a serious gap between the screen and the body.

It was clearly worse than the battery that came with my refurbished (!) phone, which never did that; it just couldn't hold a decent charge anymore. I won't even go into the absolutely ridiculous experience I had with the repair shop, like not honoring booked times and whatnot and having me wait in line for ages, both to drop off and pick up my phone.

My current phone has lost some of its battery health as reported by the OS, but still gives me over a day of use, but when the time comes to fix it, I'll go directly to Apple.

Same with laptops btw. I once caught a seller where the webpage and sticker said 5200 mAh but acpi -i reported 4400 mAh. They provided a replacement free of charge, presumably their supplier scammed them in turn (it was a small local webshop), but that replacement also wasn't great even if now the chip reported the expected capacity. Never once have I had good experiences with replacement batteries, I really wonder what they do with the originals to make them so vastly superior

Also quite noticeable that the laptop battery market became much smaller once the batteries became an internal component (around 2015) that you can't see without opening it up completely. These also used to be behind a slider or two

People don't dare unscrew electronics, even if it's about as trivial as replacing a light bulb in a fixture that requires removing a screw. With phones having the battery inside as well now, not above the sim tray for example, I wonder how much such legislation is going to help the average person