You're absolutely right! There can be major differences in the needs expressed from one technical group to any other, charged with supporting different system and/or subsystem components of an Image. In such cases, a 'Fully-Integrated System Test' just won't cut it. What is likely needed is a set of straight forward, component by component, 'Unit Test's. These tests are both interactive and recursive, so you can test, fix what's broken, and then test again, repeating this as often as is needed.
ICE/SUBS, by design, integrate directly into the ICE/IFO Component Inspectors. This allows your staff, for example, to inspect and fix problems in a VTAM configuration without concern for the operations of z/OS Members, JES2/3, TCP/IP, TCPDATA, OMPROUTE, CICS, TELNET, FTP, E/SMTP, and more.
Yes, you're right, there is more to our Unit Testing Platform than z/OS, JES2/3, VTAM, and TCP/IP.