Hi there
So what you looking for is a persistent storage, which is not supported for arch-base system because of lack of compatibility. Debian based systems have kernels which are patched and prepared for this use case.
However… arch-based systems have another method called alma
, where you can make installation on an image file on your local machine and after installation, just write it to the usb stick (it will use f2fs filesystem which performs better on flash drives) .
Of course there are some little tweaks needed to make it run faster for lower disk I/O, where actually the bottleneck is located. But hey you can at least configure the system with you preferences and remove everything what you don’t need, to make it faster.
With iotop for example you can look for programs which reads and writes a lot to disk in the background.