No one complaint about the thickness and if you were to put a ratio on it, I’d say for every twenty people who I hear complain about battery life, one complains about weight.
That’s being generous. I’ve never (unless you count this one) had a conversation with anyone who has complained about a phone weighing too much.
Batteries lose a minute amount of capacity each charge cycle, and a bit just from “time”. If they put a battery in your phone that could start off lasting two days of pretty heavy use, then the charge cycles would reduce (less battery wear) and the usable life (even at half capacity it would still last an entire day) would significantly grow. So the real reason Apple or Samsung doesn’t give you a big battery is because the planned obsolescence would go from a few years to like five years, and they want to sell you more phones than that.