the stated solution is to "load the file contents into RAM at system bootup"

Wait, so you want games on your hard drive because SSD space is too expensive (~55€/TB), so then you permanently occupy some RAM instead (at ~6500€/TB)?

Have you tried doing a linear read from disk instead, like to use zstd for good compression and fast decompression of the Factorio data folder and then make a Factorio shortcut that does like:

    $ cat run-factorio.sh
    mkdir /dev/shm/factorio
    cd /dev/shm/factorio
    tar xf ~/games/factorio.tar.zstd
    /dev/shm/factorio/bin/x64/factorio
    # the above line will block so long as the game runs
    tar c . | zstd -T0 -19 > ~/games/factorio.tar.zstd
    echo Finished saving Factorio data back to disk

such that all reads on startup (and beyond) will be from RAM but only while you are actually running the game?

>Before the optimization, the game took 113 seconds to startup1. After the optimization, the game only took 30 seconds. The script takes 230 seconds to run, much higher than the time taken for the game to load probably because the game only loads parts of the files whereas the script always loads the entire file contents into RAM.

Basically, if you want just play:

Time to play - Your script - 230s + 30s = 260s total

Time to play - Filesystem - 113s = 113s total

For permanent speedup, lets make Factorio fly with ZFS and ARC/L2ARC:

https://www.45drives.com/community/articles/zfs-caching/