When my wife, daughter and I take gyms, we typically will train them up so that 4 other Instincts can quickly and easily occupy and help defend.
For example, 2 of us will drop Dragonites into the gym, then all 3 of us will start training it up to 12,000 prestige using Lapras. Finally we'll drop a Blissey or Snorlax in under the Dragonites and move on. If 4 Instincts show up in time we get the gym quickly to level 7. If other teams want to beat it down they'll have to go through the Blissey or Snorlax multiple times.
Besides Dragonite/Lapras, teams also can use:
Tyranitar/Machamp
Gyarados/Jolteon
Rhydon/Vaporion
Exeggutor/Pinsir
Scisor/Flareon
Anyone have suggestions for other pairs that exploit the double weaknesses of high CP Pokemon for rapid training?
Good strategy. I have looked through gamepress defender's list, i think, you already have named all the relevant pairs.
Edit: If you take the wider definition of "double weeknes" with attacking super effective into a pkm and resiting its attacks, there are many more viable pairs, including
vaporeon - venussaur
flareon - vaporeon
steelix - flareon
