The other aircraft that have tried to be THE combat aircraft have often done quite well, albeit after a period of adjustment which can last a long time - and don't forget that with the lack of overt struggle like either an active war or the Cold War things may well take longer - but the Tornado, the Typhoon and F-18 are all really quite decent aircraft these days. The Harrier did likewise (being British I have more of an interest in the F-35B than the other two models).
In terms of needing to rapidly upgrade in the event of an unexpected "hot war", the upgrades developed for things like the F-15 for export could probably be relatively rapidly rolled out while a lot of trainer aircraft can easily have a light bomber/COIN role - like the BAe Hawk.
I'll post with a load of photos in a separate post...
I'll argue your central point here, doc.
the F-18 was designed as a light interceptor for the U.S. Navy, to give them an equivalent to the F-16 without forcing Admirals to pay for Air Force planes. (Seriously, that's what got it the job), and was based on YF-17, which was head-to-head against F-16 in development for the light interceptor role.
Harrier was intended as a ground-attack and short range plane, performance in the Falklands had more to do with how bad the Argentine military was, than how great the Hawker Harrier was. (thus, why RAF still ran F-4 phantoms until the Tornado, and Fleet Air Arm didn't give up theirs until they retired their remaining big flattop for a ski-jump 'baby carrier' in the eighties). and Typhoon? was developed as a compromise with dwindling budgets and reducing foreign deployments-an interceptor to carry bombs and have parts commonality with the rest of the EU.
NONE of those planes were developed with the express intent of "Being all planes to all users" as F-35 (and F-111 before it) were. Notably, th e best planes to DO that, have been planes NOT
initially developed for it. F-15, F-16, F-4, Tornado, etc, etc to F-5 and Mig-21, have all made bones in "mulitirole' but only after demonstrating airframes and base architecture that could DO THAT.
from a base of specific, core engineering. planes sold to procurement agents as 'be all end-all' generally have service lives like F-111, that is, aside from the suckers who bought them on promises (or at steep discount) they're not particularly effective OR successful, because instead of having a base of something they do well that can be expanded, they have a menu of things they do
poorly and a huge maintenance budget for doing so, often with more extended stays in the repair shop that would be reasonable for any single, semi-specialist, airframe with a similar role. (F-111 again, it wasn't until the eighties, twenty years after procurement, that it found a role it could do well, and it took that long to get the basic airframe in condition to where flying it wasn't hazardous to the crew in PEACETIME. 25% readiness figures. that's 1 out of 4 airframes are airworthy in FRONT LINE UNITS.)
England got suckered, so did we, the 'vision' of 'perfect multirole' is like perpetual motion machines, nuclear fusion powerplants, or Bussard Ramjets-it only looks good in theoretical studies, by people who don't have to make it actually function (in this case, in ANY role.)