Some missions ARE too hard.
I don't see how the majority voted "generally balanced", maybe you didn't play on 'Reality' difficulty, the hardest.
I haven't completed my re-run of the completed Blue Planet, right now I'm playing War in Heaven Act 1. The mission I've encountered that I still have not beaten on 'Reality' difficulty is 'The Plunder'.
This mission, is absolutely ridiculously hard difficulty, and I'm not a fan of lowering the difficulty level just because one mission was to hard.
If some missions are to hard, that should be a pointer to that some ships, mechanics are unbalanced or the mission itself unbalanced. All missions should be a winnable scenario even if it seems impossible at first, otherwise it would seem weird the story would even progress.
Regarding the mission 'The Plunder', I've had over 50 retries and still not beaten it. There are several factors I've noticed that makes this mission incredible hard.
On 'Reality' difficulty, the cruisers and corvettes are packed with AAA beams, lasers and all kinds of **** to rain hell down on figher squadrons. Your chances of survival are near zero if you try to get close, which you have to in this mission, to 2 cruisers and 1 corvette. I think the corvettes and cruisers have to many guns fitted on their hull, and their aim way to good.
You need to disarm the beam cannons, and shoot down the Aurora fighters (all close to the cruisers) and disable the communcations on the cruisers and corvette, while the game also has events where several fighters will chase you down, instead of randomly targeting different ships.
Or maybe that's just how if feels, but I'm consistently killed by Scorpio wing when trying to disarm the beam cannons on the Siren ship.
I mean there is much more to it than this that makes this mission ridiculously hard.
Come on, can someone just record playing this mission on reality? I bet you won't be able to beat in one go, and if you do I wanna see what tricks you used.