[moonpie@osiris ~]$ du -h $(which filelight)
316K    /usr/bin/filelight

K = kilobytes.

[moonpie@osiris ~]$ pacman -Ql filelight | awk '{print $2}' | xargs du | awk '{print $1}' | paste -sd+ | bc
45347740

45347740 bytes is 43.247 megabytes. That is to say, the entire install of filelight is only 43 megabytes.

KDE packages have many dependencies, which cause the packages themselves to be extremely tiny. By sharing a ton of code via libraries, they save a lot of space.