If anything, being constantly connected is a risk factor for batteries, not a boon. If your laptop is constantly connected (mine usually aren't anyhow!), your battery will likely degrade faster due to the interacting effects of higher heat (because laptops run in higher performance modes usually when connected to the grid) and high voltage across the cells (because laptops usually charge to close to 100% when connected).
But nowadays we have tons of Li-ion devices; compare to pretty much any. Battery robot mowers, cars, hedge trimmers, roombas, dust devils, home automation stuff, bikes, and of course competing phones. I've never owned even a single device that degraded as quickly as iPhones a few years ago; not one; not even close. And you don't need to take my word for it; Apple eventually admitted the faults, right?
But nowadays we have tons of Li-ion devices; compare to pretty much any. Battery robot mowers, cars, hedge trimmers, roombas, dust devils, home automation stuff, bikes, and of course competing phones. I've never owned even a single device that degraded as quickly as iPhones a few years ago; not one; not even close. And you don't need to take my word for it; Apple eventually admitted the faults, right?