You think Raspbian is simple?
https://www.raspberrypi.com/software/operating-systems/
« Raspberry Pi OS with desktop and recommended software
Release date: March 15th 2024
System: 32-bit
Kernel version: 6.6
Debian version: 12 (bookworm)
Size: 2,678MB
»https://www.riscosopen.org/content/downloads/raspberry-pi
« Complete SD card images
RISC OS Pi
2024-04-28 06:15:00
For Pi Zero & ZeroW & Zero2W, Pi 1 models A(+) & B(+), Pi 2 model B, Pi 3 models A+ & B(+), Pi 4 model B, Pi 400, Compute Module 1 & 3(+) & 4.
Version 5.30 Size 155.1 MB »
2.6GB of code, vs 155MB.
It's nearly twenty times bigger.
17.25x as big. And yes, I chose the image with "recommended software" because that 155MB RISC OS image is packed with dozens of apps as well.