Why compare a "full-featured", do-everything OS like Ubuntu with something pre-systemd when you're concerned about memory consumption?

I just checked a random debian 12 system (with systemd) running a bunch of services at home, and here's what I see:

$ free -m

total used free shared buff/cache available

Mem: 3791 320 2235 1 1313 3471

Swap: 99 0 99

Seems like usage is pretty much on par with your expectation. The largest consumers are systemd-journal which is storing logs in RAM, and filebeat which is relatively wasteful w/ memory. systemd itself (without the journal buffer log) consumes maybe 20-30 MB.