For me its been quite the opposite on our current game project, as it is far more larger and complex then our OS.while I spent only half time on it compared to all my OS work, which isn't exactly something to show off with yet.
Apart from that, you have libraries and tools at various levels in the game development world, which lack in OSdev world.
In any case, you are correct in that at least in the game dev world we have things to build ontop of, while the OS dev world we start from nothingness besides the Bios interrupts.
imo they both have their own unique challenges that make them both complex in nature, and in their own unique ways.