I have an Apple laptop that is a few years old. It does not have shit battery life. Probably 90% of new.

Did you research this statement before making it?

Yep. Apple battery health in system preferences will show you how much the battery has degraded since the device was new. My ~2yo M1 MacBook Pro still has 92% capacity compared to when it was brand new.

I don't know if it's in System Preferences, but for me, System Information shows my mid-2015 MBP (running macOS 10.14.6 Mojave) still has a battery capacity of 8266mAh and a remaining charge of 8079mAh at 100%. Compared to the advertised capacity at launch of 8755mAh, that's a charge capacity of ~92% after ~five years (AppleCare replaced my battery during their recall). MacBooks are just built different.

I've owned several Apple laptops over the last 20 years for both personal and work use and they've all had reduced battery life over time. I've suffered one recall, another one which failed 1 month past the warranty and which the Apple Store said was quite normal(!), and several had degraded to the point I had to ensure they didn't drop down to below 20% (or some other magic number). After the first few I took into the Apple Store only for them to say "oh that's to be expected" I stopped going in. Not sure why people think Apple laptops are magically immune, they're not. They suffer battery issues just the same as other brands do.

Apple introduced battery charging limitation feature on MacBook in 2019 (or a few years ago?), while Windows laptops supported it in 2000s. That should be the reason for previous experience. https://support.apple.com/en-us/HT211094

Device manufacturers can engineer for longer useful lifespan by oversizing the battery, can't they? Do they all do that to the same extent?

To an extent, there's a limit for air travel, generally speaking as they can be dangerous. The m1/m2 are just killer in terms of lifetime and usage for general reading/browsing/email.. and still very long for even content viewing. Most people aren't rapidly draining their batteries, so the longevity gets to be a bit better overall.

AMD is getting pretty close and the perf:watt on the coming generation(s) for laptops (including integrated gpu) look to be really impressive to say the least...

They can also implement better battery management technology (cooling, charge rate curves, keeping the charge between 10%-90% instead of 0-100%, but reporting 0-100% to the user via scaling), etc, etc.

For a good counter-example, look at the early Nissan Leafs. They burned out their batteries in a matter of a few years, but battery replacements for other brands from that time are basically unheard of. (The inherent information asymmetry for new car purchasers is one reason Biden's IRA dictated minimum car battery warranties.)

Funny, I heard the total opposite about Nissan Leafs. The industry was guesstimating that batteries would last 8-10 years. The first Nissan Leafs (which was about the first commercially mass-available EV) had battery lives where something like 90% were still going strong and still 80% of original capacity left after 13 years.

Rather than the Leaf being problematic, it was the car that showed the market that worrying about the lifespan of EV batteries wasn't really necessary.

I had one of those early Leafs, the battery degradation was real. Newer vehicles seem to have much better curves.

Modern Macbooks are very strategic about when and how much they charge. You can override it if you know you need a full charge Right Now, but otherwise they will decide how much to charge based on your usage patterns, which keeps the battery alive much longer than on many other brands of laptop.

Apple's batteries are covered under warranty up to 1000 cycles. I had them replace my battery that hit 80% capacity at 3 years right before AppleCare ran out.