It would be a disservice to truth to define it as the average of all possible lies.
As an example, let’s look at dishonesty in politics. It has been a rather common occurrence in government and among politicians that the ruling party paints a rosy picture of the results of government policy and the opposition a dreary one. In most cases, it’s not because of their biases; it’s not that the ruling party sees the truth with a positive bias and claims that things are relatively better and that the opposition accordingly applies their own negative bias to the truth. Often instead, they claim what they claim irrespective and regardless of the truth. For example, if the economy was doing great, the opposition could still claim that the budget is terrible — and if the economy was in the doldrums, the ruling party would still fudge numbers to make things look good. The truth isn’t always to be found between the lies of two dishonest opponents.