They have. The iphone 6 was I think the thinnest iphone at 6.9mm thick. The X was 7.7mm, and the 15 is 7.8mm thick. And at least for my use I do get 2 days of battery life. Even with the 80% charge cap.
Overall phones have been getting chunkier, larger too. I dislike the size, but like the added battery life from the thickness is nice. My pixel 8 is perfect in both regards for me :)
Edit: just saw the sub. Don't really know a lot about apple phones specifically.