The Pixel 6 brought 5 years of software+security updates; the 8 brought 7 years. The 6 started using semi-custom Samsung soc. 8 brought new security features at the hardware level. Beyond that, minor changes afaik. 6 Pro brought true zoom (I really appreciate it), there's a few features that need the 8 soc for "ai", variable refresh rate on the 7 (I think), higher+lower vrr on the 8, etc.
I upgrade regularly: whenever an interesting feature or security improvement is made available, or if a family member needs a new phone (I get the new one, they get my used). Nexus 4, 6, 6P, Pixel 2 XL, 3XL, 5, 6 Pro, 7 Pro, 8 Pro. Toss in the Nexus 7 gen 1 and 2 (cellular) too, and my days of having a conversation with a tablet held to my ear for calls. Family is all pixel 6 or newer right now, and shouldn't need to upgrade for another 2.5y.
I’m on a five year old iPhone XS MAXXX and it runs like a brand new phone, and the battery lasts all day. I’m only considering upgrading because I’d love a 120hz screen and USB-C.
I agree with ya but I still used my 5s for 4.5 years! They replaced my battery for free out of warranty cuz the batteries were shit on that gen, though. The power button got all fucked up after that too, but I used onscreen controls to mitigate that. Woulda been cool to have that fixed too, but at they point I wanted a bigger screen.