No, you are never specifying to actually upgrade the package with the ‘u’ flag. Running pacman -Sy archinstall
would upgrade the package, since it would first refresh the package cache then reinstall the latest version.
Also, there’s not really a benefit to using 2 'y’s but it does add some extra stress to the package mirrors, so I would avoid doing that.
The big thing it has going for it is that they set up btrfs snapshots out of the box so you can rollback if necessary.
They also do more automated testing than Arch so theoretically it should be more stable.