Apparently they are fan-made missions (added by the Silent Threat expansion), selected to the game by some mission design competition held by the publisher back then. That's the impression I got somewhere.

They seem ok, but now I am stuck in the third mission. It seems quite a straightforward mission, just destroy all enemy fighters and three bigger ships... but the enemy fighters appear at a fast rate so I think suddenly you and your wingmen are surrounded by like 16 enemy fighters who are very persistent... Oh well.

Either I am a very crappy player, or there is a huge difference with the enemy capabilities between Normal and Insane difficulties. As I told earlier, I destroyed Hades already on my earlier attempt and there were only two badly injured (Loki) fighters left after Hades blew up, so instead of jumping out I still decided to destroy them, and then jump out.

I got one of them to engage me, I thought it would be an easy fight as it had mere 3% hull left... yet the bastard killed me in like 10 seconds or so. I took first some damage when fighting it head to head, then when I tried to avoid its hits and fly in circles, it seemed it was still constantly hitting me very accurately, I was unable to avoid its shots no matter how much I tried to turn to different directions.

Not sure if their guns are more powerful in Insane, or if they just are that much more aggressive, or what... Mind you, in many other missions I didn't have similar dogfighting problems, but in the last mission the enemies just seemed very aggressive and persistent.

I think there is a gap in difficulty between Normal and Insane. I remember the ST escort mission you mentioned, where you need to get the escape pods way over to the jump point; I could usually save a few, but I think I replayed the mission until I was able to save them all, and it was still very irritating (especially trying to knock out the initial waves of enemies, when you first need to get into position).

Quite probably a combination of stronger guns, better fliers, and more aggression. Also, I seem to recall the Loki's always spawned at something of a distance in the last mission, so I'd have a little bit of time where they are basically coming in straight at me.

I don't think I'm a great pilot, and I certainly wouldn't have had the patience to plow through Insane like you did.