A game, where pirates left for a longer time were VERY big danger. I remember how many fleets I've lost when Pirates weren't destroyed fast. Not only their invasions, but also simple visit in their sector was a great impact for my fleets then.
Scourgeclaw, going back to Homeworld 2, isn't that one of those missions where you MUST BE HIDDEN all the time? Also, you must keep in mind you need to have take care about the ships, as they come from mission to mission. Any loss may impact your next missions.
Still. It is nothing compared to Homeworld, where Battle over Hiigara (last mission) was VERY difficult, unless you were capturing ships aside of production. The only game I have finished without crying and cursing was... Homeworld Cataclysm. But its because it had different levels of difficulty, YET it is ex-equo on first place with Homeworld (1) if it comes to plot and voice acting. The Beast is one of those rare enemies in games that I have truly hated and feared in the same time.
Even the Borg from Star Trek or these guys from Babylon 5 I can't recall are just silly-looking when compared to The Beast.