If you use the archinstall script to save time on manual installation, I think that’s reasonable as long as you’ve adapted that script to your needs and decisions about the system. I repeat, archinstall makes its own default configurations in tools that the user must configure in the post-installation, such as security and system recovery. Archinstall does not configure selinux, snapper in grub, etc., and for this you have to partition the disk in a specific way, not as archinstall does by default.

Yes, if you use Arch, a DIY system where the user decides which services to activate and how to configure them. Archinstall decides for you how to partition the disks and which services need to be configured based on the options you choose. In other words, Archinstall offers the same thing as an installer like Calamares, but in a CLI script. However, once the base system is installed, you must manage the security tools, backup, etc., not the distribution developer.

If you installed it using the archinstall installation script, I believe you. If you did a manual installation of Arch for the first time, I don’t believe you installed the system in 15-20 minutes.