Pentesting itself can be quite a broad field, and although you’re right about a lot of it being network-related, it typically gets split into categories depending on the exact type of pentest (e.g. application penetration testing, wireless pentesting, embedded devices, SCADA/OT systems).
You could get into a debate on which areas are more demanding, but as you get deeper, they do require different skill sets/specialities/ways of thinking. Someone who’s great at web app pentesting may not necessarily be fantastic at RE or social engineering.
Compare that to say, cryptography or code review, which typically require fairly deep specific knowledge and a lot of intense focus, as opposed to broader knowledge and a willingness to try a lot of different things.
Most findings in netpen reports I see are basically that something wasn't configured correctly, or that one of the 10k employees had a weak password, or someone got phished. I often chuckle but rarely am surprised or learn too many new things.
I googled, but I didn't manage to find out what "netpen" is. Network Penetration? I'd assume that virtually all relevant security stuff is network related these days so I'm still confused. Which are the other specialties and why are they more demanding?