Niri is RAM efficient. I run Niri in an 8GB VM on Intel Macbook, and on a $99 8GB mini PC. Total RAM usage on boot is less than 400MB with waybar, polkit, ssh-agent, mako ... That's in the ultra lightweight WM category. Compare that to Gnome+paperwm (1.6GB) There are features Niri sorely needs: 1) 2D overview (zoom in/out), 2) enhanced meta for windows (to create window indicator [1] and window picker)
We're calling 400MB RAM usage ultra-lightweight now? OpenBox needs 7MB of RAM, and there are WMs that are even lighter on memory requirements. > Compare that to Gnome+paperwm (1.6GB) Anything seems lightweight if you compare it to a DE well known for its bloat.
A minimal Niri functional environment is similar to IceWM in RAM usage. I used to run antiX in VMs.