This is complicated by the fact that ‘political knowledge and skills’ are not consistent between careers

Also (and I suspect even more importantly) by the fact that the impact of political knowledge and skills may be different in different careers. Not only because some careers simply have more room for variation, but also because some careers have more scope for effective evaluation on non-political factors.

I suspect that both engineering and novel-writing have lower impact-of-politics than average, but even though novel-writing is higher-variance I suspect that there's more scope to turn political skill into career success in engineering than in novel-writing.