Is the Growler "lacking"? Or is it just that the Prowler, at this point in time, more capable?
Its a development "point in tme" issue more than anything.
the airframe of the Prowler is/was functionally more efficient so had more real estate available for its ewarfare suite. Its suite is designed around a 3 man team so is optimised around that construct, and at the time of its development it had a specific design intent.
the Growler was never going to be a direct 1 for 1 replacement for the Prowlers mission set as they have different requirements.
Hoever, add in miniaturisation advances and sensor advances and the 2 man crewed Growler starts to exceed the Prowler in some areas, even though it may not be as effective in "all" of the Prowlers design role.
But, and its a big BUT, once the design architecture dvelopments for the JSF leak through to other opportunities (and a classic example is the advances and improvements that JSF has provided to another distributed architecture sister - F22) then the Growler will leap ahead pretty quickly. Those advances and developments start to take away the need to deliver an ewarfare capability to the same CONOPs requirement of the Prowler.
The wild card would be a backseater version of the JSF. I'm not totally convinced by the development of a singler seat JSF ewarfare platform, you can only hand off so much to the system at an ewarfare level, and IMO trying to get the pilot to rely totally on an autonomous ewarfare suite would be folly. We are already seeing how NOT to do this so after all the lessons learnt that are available, I cannot see the US making a single seat JSF ewarfare asset (and for convenience and artistic license, lets pretend its called a "Howler"
A JSF already has a sensor and ewarfare capability that exceeds what any of he F-teen platforms can deliver, and you cannot at this point retro build DAS etc into an older platform, its a distributed design and its built into the architecture of the plane itself. However a JSF already has the basics of elements like DAS which no other small 1-2 man fighter even remotely approaches. If you start junking thinks like the STOL elements that does give you real estate for extra and more pwoerful ewarfare elements, but its still relies heavily upon automation at the platform level. That kind of ewarfare dependancy is dangerous - irrespective of whether the technology exists to start taking up more and more of the backseater roles, the legal and operational constraints are not conducive to it.
At the end of the day its about he capability set and requirement, and just like CAS and maritime strike, its no longer about the platform built to do a role, but a platform that has the flexibility to provide an extra contribution to the capability and operational need.
We're already seeing this at the ewarfare level as the advances in tech and capability are seeing a reduction in the need for dedicated ewarfare platforms and an increase in the development and training for pilots and crew in smaller assets pick up those specialised roles. One is not a replacement for the other, but the brooader system design is now about literally anything that is in theatre should be doing more than just its main task, ie they are all contributing feeds into the broader warfighting picture. that goes for air land and sea assets.