An RTOS compared to an OS like linux basically just means it is deterministic, you can guarantee some interrupt is handled within a certain time. Not necessarily faster
Actually, what kind of stuff other than the stock market actually cares that much about strict determinism and task priority? Only, other that really suggests itself is schedulers for multiple groups running big iron tasks, rather than micro-controllers.
Not familiar enough, just doesn't seem like there would be a lot of groups fighting about priority on micro-controllers. Usually seem very focused and single task specific anyways.