C-3PO is a pretty sophisticated piece of kit. Not only does he know six-million forms of communication and act very convincingly like a nervous butler, but he seems to be a tactical statistician too.
There is a huge difference between being a statistician and being a tactician.
I can tell you that the odds of dying in Russian Roulette are 50% (assuming you play the game between two opponents, alternating shots until one dies). But that is not the same as telling you whether you should play Russian Roulette or not.
Similarly, I can tell you the odds of drawing a given hand in poker, and the odds that your opponent has drawn a better hand than you, but that doesn't help you with deciding on how much you should bet.
C3PO is logical in nature, and is therefore inherently capable of analyzing what he perceives. Assuming that droids still use the underlying principle of computing (which seems fair to assume), every computer (in the broad sense of the word) analyzes its input in order to render output.
C3PO has shown to be capable of doing more than just his primary purpose. He can have meaningful conversations (unrelated to his primary purpose), he can learn, he has opinions, he can be sarcastic or wistful (mostly to R2), he is shown to (at least try to) be a fair judge of character. This proves that C3PO is technically capable of learning anything he wishes to learn (as long as his body is not physically incapable of it, of course)
If anything, tactics is about playing the opponent, instead of playing the odds. This is almost perfectly encapsulated by Han's well-known quote:
Never tell me the odds.
Notice that Han doesn't say that C3PO is wrong, he merely dismisses it as irrelevant (to him). Han is an emotional character, not a logical one, and therefore has no use for C3PO's statistical feedback.
A slightly more direct answer
While it is true that tactics are often influenced by the odds of success, that does not mean that the odds of success are the sole factor in deciding your tactics.
C3PO is good at one skill (calculating odds). But he has no military expertise, nor is he particularly experienced in combat or navigation.
Sir, the possibility of successfully navigating an asteroid field is approximately 3,720 to 1
C3PO has little to no navigational skill. It is very likely that C3PO was listing statistics of past events (e.g. of all recorded flights where a ship manually navigated an asteroid field, only 1 out of every 3721 flight records did not mention a crash).
That says little about the current situation:
- Han's skills
- This particular asteroid field
- The hull strength and maneuverability of the Falcon
- The inherent dangers of not flying into the asteroid field
- ...
All of these factors can influence the odds dramatically. If C3PO is listing statistics based on past events, then he is overgeneralizing.
Edit
If this overgeneralization is the best that C3PO can deliver, then I do believe that the Dunning-Kruger effect applies to the justification of why C3PO is speaking at all.
If C3PO is not aware of any better way to help, then he must logically believe that his way is the best possible way to help; which leads him to speak up about his statistical findings.
This seems logically valid. Because if C3PO was aware of a more meaningful response, there's no reason for him to not give that more meaningful response.
Edit - A bit of offtopic pedantry
Sir, the possibility of successfully navigating an asteroid field is approximately 3,720 to 1
This also hinges on what C3PO means by "successful":
- Not hitting a single asteroid
- Not damaging any ship systems (but possibly hitting a few asteroids)
- Not rendering the ship inoperable (but possibly somewhat damaging it)
- Not killing any passengers (but possibly rendering the ship inoperable)
- Not losing your way (which seems the most literal interpretation of "successful navigation of an asteroid field", completely disregarding ship damage or loss of life, though it does seemingly exclude rendering the ship dead in the water)
The usefulness of his statistical analysis very much hinges on his definition of what constitutes a successful navigation.