I used to write freelance for Shadowrun 3rd Edition! I wrote the section on The Republic of Québec in Shadows of North America and I also had a mechanics section in Sprawl Survival Guide. I also wrote freelance for a bunch of other stuff back in the day, in addition to working for a shoujo-inspired TTRPG company.
That was all in the late 90s and early aughts though; since then I've mainly played in games and DMed them instead of being on the writing end.
I get what you mean though; it's really nice to be able to work out a story without so many moving parts that are out of your control. Though to be fair, I was always the very narrative kind of gamemaster: always working with players to tell cool stories and make sure everyone had fun, and less being concerned with numbers or balancing.
I'd love to play in more TTRPGs these days but to be honest I've got so many things going on that it's hard to commit to something that regular x_x
I really need to clear up my to-do list...
