I'm interested in, and started this thread to discuss, how it's absence would have affected 4th, 4+, and 5th generation fighter design.
OK, I'm onto it now.
I think the most profitable example is the F111B/VFAX/VFX vortex in the 60s, the last fighter type before E-M and the almost contemporary of the first E-M fighter the F15.
When it became apparent in the early 60s that the F111B would go ahead the Navy started the VFAX competition to replace the F4 in the escort/air superiority fighter and ground attack roles, working alongside the F111B in CVWs. The 1966 VFAX spec demanded it be able to beat the Mig 17 and Mig 19 in close combat, and the 1967 spec demanded later Soviet fighters, as well as undertaking the attack missions of the A7.
In parallel Grumman was working on the F 111B, trying to reduce weight, and was contracted by the Navy to undertake studies of advanced fighters. In the event the VFAX proved to be a dud, not better than the F4 as a fighter or the A7 as an attack aircraft. In the process Grumman came up with design 303 and in 1967 reworked this design to include the AWG9-Phoenix system.
As a result, bearing in mind the problems with F111B which was pushing it towards inexorable cancellation, the Navy was presented with the answer to both of its problems, a replacement for the failing F111B and a replacement for the F4 in the escort/air superiority role. The F111B was cancelled and a month later the Navy issued the VFX requirement written around Grumman design 303. 6 manufacturers submitted proposals but Grumman's 6th refinement of 303 won the competition.
So basically the F14 is an escort/air superiority fighter with interceptor equipment squeezed in. I'd suggest that this was about as early as this could be done; the Tomcat used new turbofan engines, extensive titanium, newly developed swing wings and innovative aerodynamics. Coincidentally the USN decided to use the USAF upgraded A7 themselves, covering the loss of the 'A' portion of the VFAX.
Basically in my opinion even without E-M maneuverable fighters would be built because they could be.