Eliezer, I agree that exactly even balances of evidence are rare. However, I would think suspending judgment to be rational in many situations where the balance of evidence is not exactly even. For example, if I roll a die, it would hardly be rational to believe “it will not come up 5 or 6”, despite the balance of evidence being in favor of such a belief. If you are willing to make >50% the threshold of rational belief, you will hold numerous false and contradictory beliefs.
Also, I have some doubt about your claim that when “there is no evidence in favor of a complicated proposed belief, it is almost always correct to reject it”. If you proposed a complicated belief of 20th century physics (say, Bell’s theorem) to Archimedes, he would be right to say he has no evidence in its favor. Nonetheless, it would not be correct for Archimedes to conclude that Bell’s theorem is therefore false.
Perhaps I am misunderstanding you.
The error here is similar to one I see all the time in beginning philosophy students: when confronted with reasons to be skeptics, they instead become relativists. That is, where the rational conclusion is to suspend judgment about an issue, all too many people instead conclude that any judgment is as plausible as any other.