I might be speaking out of turn here but I seem to recall that the Concorde designers were more aware of the material temperature limitations as a primary limiting factor in the upper speed ranges.
If so then they would probably have designed the airframe to achieve its performance in a speed zone convergent with the temp limits.
As in designing the high speed, high alt 'coffin' corner to be wide enough to be acceptable in all control configurations at or near materila temp limits...yet not so wide as to provide excess redundancy. No point in having a limiting M of 2.5 if you know that in pretty much all coniditions the max temp limit of the pitot is exceeded and hence you will damage it.
However the U-2 and SR-71 were max performance driven designs... the highest possible, the fastest possible, hence in the SR-programme the development of a whole range of new materials, production methods and assembly technology...to say nothing of mechanics tools and so forth.
It then follows that to reach those extremes the margins are far slenderer and the aircraft will be operated far closer to those limits.
As for the low speed behaviour of the Concorde ogive, initially the on paper design was not brilliant. The prototype wings were revised to produce the pre production items which were further refined to give the definitive production items. Each iteration was primarily aimed a improving the low speed performance whilst retaining the lowest possible effect on the high speed performance. If you get a chance look at them look particularly at the camber and twist of the outer portions of the leading edge.. on 002 a Yeovilton its a pretty simple transformation, slightly more complex on 01 at Duxford and a whole heap more complex on the production wing.
Great stuff empirical design.....
Just on another note...swept wings/ swing wings....The F-15 and F-16 are almost a generation later in engine design than both the F-111 and the F-14, both swing wings....hence the additional power made it possible to achieve the limited high performance required of the airframes without resorting to swing wings or true swept wing (the leading edge is swept but trailing pretty much straight).
And the F-14 can certainly give the F-15 a run for its money in a dog fight...and can certainly out last an F-15 in terms of loitering performance... as it was designed to do.
However I agree that with improving engine technology and computer enhanced stability the purely mechanical advantages of the swing wing design and true swept wing design will be questioned, certainly in smaller agile combat aircraft. It really boils down to the size of the perfrmance envelope demanded by the aircraft. As it expands in all directions the advantages confered by one or other physical configuration will be diminshed to a point where it is no longer justified.
Conversely a very focused and defined envelope (like a subsonic or even supersonic commercial airliner) will benefit from a physical configuration tightly tailoered to the envelope, afterall pulling 6 g at high Mach low alt is not on the cards....but efficient cruising and 'stack' performance are..