OK, you're right about this mission being easy. I've took a break, then changed an ingress vector and got in. The only difficult part after fighting the fleet is the egress, which I've got wrong on my first try (though maybe on lower difficulties, briefly flying into Amaterasu's flak pocket and is more survivable). Other than that, my leading cause of death were spontanous explosions, which I suspect to be debris collisions. I might've just been really unlucky regarding that, but those were rather annoying. Also, it seems that if you skip the fleet, it'll get destroyed anyway. Those cannons do an impressive job at killing everything that comes into range.
Also, it disappointed me a bit that the campaign simply ended after that. I kind of expected that there'll be a wacky Gradius homage (yes, I've looked through the assets), some (more) time travel, a wacky Thunder Force homage and an unexpected twist ending. The modpack contains about twice as many assets as the campaign, and plenty of things are left hanging. A sequel would really be appereciated.