Reminds me of the occasions when iphone customers complained about their battery draining faster / their phones lagging after a software update for years, and just recently apple responded: “you can have battery or features not both lol”.

Regarding features: Usually good software development makes the software more performant over time, not less. But customers are expected to react to excessive DRM measures (like denuvo) or the uprising telemetry hell (like windows 11) with buying more performant hardware. Yields the question what is a (desired) feature and what is a bug, AND what is a cash cow for companies milking their customers.

My tip would be to look for replacements which are advertised to work with the specific phone model but are not necessarily original replacement parts, bc like you said they tend to be fake and of bad quality. There are a number of brands who have specialized in this market by now. There are also very few brands who sell original parts via ifixit (e.g. google for pixel phones)

Also, if you want to replace a battery stay away from samsung. They glue the batteries in so tight that you have to use alcohol to loosen up the adhesive.

Also also, if you want to replace anything, stay away from apple. They have a history of bricking devices software side if they detect third party parts.

Consider buying a phone which lets you change the battery considerably easy. I watch teardown videos of phones before i buy one to compare the process and the likeliness of me breaking something in the process. Of course not everyone is going to do this, but you could ask a friend to do it (i changed batteries for phones of at least 3 or 4 people by now).

Apple doing software updates for such an extended period of time is wild, considering how anti-consumer they are in the first place (bad repairability, walled garden, bizarre prices).

Google does 5 years updates for the pixel phones, which is to be expected since they own android lol.