only rewards a white DOff on critical success? If that's intended, it's rather underwhelming - you have to do a 10-assignment chain to open it, it's listed as purple quality, and with a purple DOff with 2 crit traits only has about a 25% chance to crit (and does not look like it rewards any DOffs on normal success).
I just finished the mission and managed to get critical success, but all I got was a white Cardassian assault squad officer.
Didin't have it yet, but it sounds a bit underwhelming considering that it took 10 steps to unlock it and the odds are way worse than through the Cardassian and Bajoran officer exchange programs you can unlock in 4 steps. Of course, you also lose an officer in those, but you can throw whites in there and usually expect to get at least a green one. And whites are at some point only 75 Dilithium or 20% of a green doff.
The chains reward is Gul Tain, the additional assignment is only a bonus.
I don't think that's in question here. A repeatable assignment shouldn't require a critical to reward a white (common) quality duty officer. Sure, this would make sense to have a chance on normal success to do that, but criticals should generally reward uncommon, rare, or very rare. That would make more sense - and be worth the time/duty officer investment.
The other rewards for the assignment are very low for the time required. The only reason you'd bother with this assignment are the chance at the DOff.
That's one (valid) argument you're making and I somewhat agree with. Though, the more compelling argument from a design/development standpoint is that the rewards don't match the outcome thresholds. Critical mission success does not make intuitive or logical sense if it rewards a 'common' reward (such as a duty officer).
Mission successes are common. Thus, the rewards for completion should also be 'common' (white/green). Critical successes are significantly less common and should reward accordingly.
Disaster (very uncommon and has some annoying side effects as a result) - also known as a critical failure
Failure (somewhat uncommon and generally doesn't have negative side effects)
Success (generally common and usually rewards something of common value depending on rarity of the mission and/or its accessibility)
Critical success - (generally uncommon and usually rewards something of uncommon value depending on the rarity of the mission and/or its accessibility)
At this point, we're not seeing the rewards matching the outcome threshold. That is why it is neither intuitive nor logical. In effect, it is adding a chance on top of a chance on top of a chance (success/failure -> critical success/failure -> dice roll on critical.) At this point, getting a 'very rare' duty officer out of that critical would be considered legendary or an artifact because the chance threshold is that small - and also need a new rarity type introduced.