I find it very plausible that [Blues] are better able to pretend to be [Greens] than vice versa. But what follows from that?

That Blues understand Green arguments but aren't persuaded by them (presumably because they have counterarguments), whereas Greens don't understand Blue arguments and this makes it unlikely they have counterarguments.

Now let's look at your three objections, near as I can tell your first objection amounts to "sometimes the people defending the incorrect position are heterogeneous, this gives them a large advantage in the test", and your third objection amounts to "sometimes the people defending the incorrect position are homogeneous, this gives them a large advantage in the test".

Now let's look at you second objection: much as it may seem that way your opponents are not evil mutants whose position has no logic to it whatsoever, most position actually held by humans, especially intelligent humans have a certain logic to them. (And if you're opponents' position really has no logic to it beyond saying anything plausible sounding that backs up their conclusion, that's very easy to imitate). Thus, the two positions have different logic to them and it will be hard for a person only familiar with one of those logics to imitate the other. On the other hand, if someone is familiar with the logic of both positions A and B, the fact that he nevertheless holds position A is evidence that A is in fact correct.