Those are filled but if an opportunity hire came along we'd hire them, so the jobs are still listed. You either need to have shipped a game or be a guild hall graduate to get a job as a world builder. Its so much more involved than people think it is. Study real world architecture, construction, and look at a lot of games.
I think we've brought on like 3 new level designers this last year and have a total of seven now. My advice is to fake it until you make it. In other words do what your dream job is at night and on weekends in your spare time. Pretty soon you will become just that, and be able to make a living at it. You have to have a portfolio full of amazing work, that is what gets you noticed. Work with modders on projects or just make your own. Two years from now you should have a portfolio full of amazing work to show off.
I haven't played guitar in 25 years and wasn't ever that great at it back in the day. I started playing 45 minutes a day 5-7 days a week and I think its my one year anniversary now, and I'm way better than I was when I quit. If you just commit to some reasonable amount of time nearly every day to practice a new craft you can get pretty good.
Judge your work and release your work as mods for others to download and listen to their crits with an open mind. That is the fastest way to improve. Start with small projects and advance to bigger ones. Make sure you finish everything, so once you finish a shed that is amazing, advance to a 1br house, then do a 2, then a mansion, etc. Lighting, detail that matters, interesting architecture, mood, theme and performance are all very important things to consider in design. Game flow as well, how does it play?