IPS vs EDR vs NAC vs RMS

InfoSec teams have only so much budget, so how does one decide on whether to spend on the outer perimeter or inner perimeter of an on-prem network?

Well, what industry are you in?  Where are your critical systems and business processes?

If your org is not highly regulated, and you have critical systems (i.e., ERP) within your inner perimeter, then that should be your focal point.

While EDR, NAC, & RMS are all sexy technologies, they serve to protect the outer perimeter (e.g., laptops, workstations, file shares, business subnets).  And while assets themselves, hopefully your IT folks have embraced the cloud and ECM / EDM (i.e., SharePoint).

For the inner perimeter, your data center, IPS, UEBA, TI, & ATP technologies may be used to protect your financial systems, etc.  Now, these solutions aren't silver bullets, but there a start.

In this age of shadow IT, virtualization, and distributed workforces, priority should be your most critical digital assets.