I haven't tried Arch, but in my experience changing those things in Ubuntu setup is simple and can be done in the GUI installer - I do it every fresh install. I haven't tried changing the bootloader; haven't had the need to.
There are many configurations that aren't (easily) possible with the GUI. The average user isn't going to care if they use LVM on LUKS or LUKS on LVM, but if you do, Arch makes it easy.
I personally prefer using EFISTUB instead of a bootloader, and this was very difficult to do on Ubuntu last time I tried.
I personally prefer using EFISTUB instead of a bootloader, and this was very difficult to do on Ubuntu last time I tried.