Designing secure network architectures
If your InfoSec learning path has been anything like mine, a load of your time has been spent learning about networking. Do Chief Information Security Officers (CISOs) talk about networking very often in the day to day? Well, yes… networking is mentioned in the LinkedIn/evening drinks/corporate "networking" type of way, but they're very rarely talking about TCP/IP.
Does that suggest that you shouldn't know about networking? Or that you should forget all that you've learned? Of course not. By knowing about these topics, and understanding the likelihood of a threat exploiting a vulnerability in network devices or protocols, along with the impact of that event, will enable you to make more informed decisions for mitigations, rooted in the principles of risk management.
In my opinion, it's worth learning a bit of everything in InfoSec, regardless of the path you currently have your sights set on following...