I don't want to sound cliché but I suspect great part of the RAM in parabola is thanks to systemd.

Don't give up on GNU/Linux, there are some distros that take it to extremes to cut the packages to minimum. Source Mage in particular has the philosophy of only including what you want, nothing more, and the sources are clean and untouched. I don't have access to my installation but as soon as I get it I will post results, meanwhile look at how some guy went to have a graphical environment with 97MB.