Alternatively, one can negotiate the desired level/salary when starting a job so you can ignore the politics at least for several years, right? Or is it as well easy to be demoted (without politics)?
For L6, for example, you might be able to convince the recruiter to set up the right interview process, but your level is 100% tied to your interview performance.
Salary is a different story--negotiate, always, but be aware level and salary are related.