A fined tuned argument.....Heywood style.

[Angrboda]

The two possibilities are indistinguishable in objective ways to determine their probability. And keep in mind we aren't talking about exact probabilities...it would be enough to simply have an objective means of showing the probability of A is greater than B or the probability of B is greater than A. We don't have that here.

That's bullshit. Besides which, if you don't have any way of determining probabilities, my first argument (here) that you are either a) making an argument from ignorance, or b) arguing on the basis of the most plausible hypothesis with a hypothesis whose plausibility is unknown, holds, and your argument fails, as neither argument can be successfully completed ('a' is fallacious, and 'b' argued using the principle of indifference yields no winner, even if accepted as an argument). [In arguing to the most plausible hypothesis, if there is no "most plausible" hypothesis, the entire argument fails as there is no reason to prefer one hypothesis to the other. If you say that there is a reason to prefer one hypothesis to the other, you've abandoned the principle of indifference. Either way, you lose.]

Besides, you gave four possibilities, so the odds of a designer are 25%, not 50%.