The fact that different Demigods have different strengths and weaknesses?
Yes, we know that. How does that help prove your point? Lets say DG build X1 is strong in aspect A and weak in aspect B. DG build X2 is strong in A and weak in C. DG Y1 is strong in B and weak in C. DG build Y2 is strong in D and weak in E. DG build Z1 is strong in C and weak in B. How does that information tell you anything about which DG counters which?
Answer: it doesn't, and in fact does not even support the conclusion that such DG X < DG Y relationships exist in the first place.
Take the actual example I gave. I really can't see how anyone other that Oak could counter 4 Reguluses. Four Oaks (it could be pulled off with 3 or even 2, probably) actually do a really good job countering 4 Reguluses. If my opponents switch to all Oaks, there's no way in hell I'm going to stay with 4 Reguluses. It's no longer an optimal combination. I'm going to switch to something else. There is too much homogeneity with four of the same type, even with different builds. This allows a specific counter that will be better, because there are certain things that each specific demigod *cannot* do, even with differentiated builds.
Lets talk about 3v3 since thats the standard format and baseline. Lets say the enemy team has 3 Regs. Number of required Oaks = 0. Number of Required *Any Specific DG* = 0. So lets say your team jumps into my game. I have about five 3-DG combinations that I am especially fond of, none of which involve doubles. Your team picks 3 Regs. My team does not change anything and proceeds to stomp you anyways because 3 Regs is bad.
Additionally, team automatch features generally do not let you see your opponents pick of race/character/etc before you are actually playing. I assume that this is how it would be done for a DG team automatch, so this behavior would never even be possible, let alone probable.