Sort of but not really. The original TACAMO's were communication relay aircraft rather true airborne command stations, so they were lacking a lot of the equipment that the E4B's and the EC-135's had. So while the other two aircraft could act as relays they couldn't act as command stations, which of course made them cheaper. It was only with the E-6 that they became full command stations. So to go back to the cold war era I think the optimum would be maybe 20 "full fat" airborne joint command stations alongside 20 cheaper relay planes. You would have the same or slightly great capability but much less cost.
I seem to recall that there were several roles for the EC135's in this context:
-Command post (ie. looking glass)
-line of site UHF communication relay (ie. Post attack command and control system ?)
-minute man ICBM launch control (I believe via line of site radio links to the missile silos in question ?)
-I may be missing some others
I'm not convincing almagmating all these roles along with the TACAMO role into one air craft would have made sense during the Cold War. I seem to recall SAC also kept EC135 air craft on alert at multiple locations so they would be close to where they would be needed, so there may have been a hard lower limit on the number of air frames that were needed ? (To be transperant I am also not 100 percent sure if there were different EC135 variants for each role but I suspect the alert basing requirements may have been important re air frame numbers ?)
During the Cold War SAC also considered the Looking Glass mission to be of paramount importantance. I have my doubts that the USAF would been keen to let go of it much earlier than they did. (I recall an account of an interview of a SAC General that basically said if the airforce could only afford one air craft it would be the looking glass air craft.)
Edit to add:
-My understanding is that SAC kept a looking glass aircraft on airborne alert on a 7x24 basis during the Cold War. I suspect this would further increase the number of air frames that were needed. Once this airborne alert requirement ended I can see a smaller number of common larger aircraft making more sense.