I highly doubt the original battery will last 7 dependable years

If they actually abide by the EU law requiring user replaceable batteries by 2027, then going forward from there I could see a more substantial number of folks keeping a phone that long.
But a sealed Pixel? By 4 years in or so when the battery dies, I don't see too many people replacing the battery in their scratched, cracked, glitchy, boring to them phone when they can pick up a shiny new one
In fact even with user replaceable batteries, that same scenario might apply. And Google may actually be counting on it lol. Like you said, promising something and doing it are 2 different things

Many other phone makers have broken those types of promises
Although folks keep iPhones around that long ¯\_(ツ)_/¯