Vastin wrote:...but the knee jerk reactions that are engendered when the word 'Nerf' is evoked, as a designer I find that fascinating, but very confusing at times.

I interpret "Nerf" to mean "weaken so much that it is unbalanced (i.e., not challenging; boring)"
By that definition, everyone agrees that nerfing is bad.
But since not everyone agrees on when a game element is "balanced" not everyone agrees on when something has been "nerfed"
Ultimately, I think we're trying to balance two things:
1. Arco should be hard enough that experienced players can enjoy the experience no matter what starting ship they choose.
2. Arco should be easy enough that novice players don't quit the game in frustration, no matter what starting ship they choose.
I'm sure everyone can understand that this is not going to be easy--particularly because the different starting ships have different capabilities.
This discussion has been very useful for me (and I'm really glad Vastin brought it up). I guess I'm made a few tentative conclusions:
1. It's hard to argue in a vacuum. We need to try some things and see how players react. Ultimately (probably in version 1.1) we will have some statistics that will help us see how many players give up before completing Eridani. Until then, I don't think we'll have hard data.
2. I do think there are some things I can do to make Arco more accessible to novice players without removing the challenge. In particular, 0.99b adds some AI to Arco so that he warns the player with a few shots before going for the kill. Novice players that are slow on the missiles will at least have a chance. [But Arco goes for the kill instantly if he is ever damaged, so hopefully experienced players will not be affected.]
3. Just to add a little bit more time to the encounter, I decreased Arco's fire rate slightly. I don't know if this makes him too easy--I'm interested in feedback.
4. As Vastin points out, the targeting ROM is a big inflection point. If the freighter gets the targeting ROM then killing Arco is almost too easy. I don't know what to do about that. I might (post 0.99b) try to make Arco shoot down the missiles if he can see them coming.
5. In 0.99a the targeting ROM actually made things worse for novice players. Since Raisu gives you Arco's habitat as a target, a novice player who doesn't know how to change targets will keep firing missiles at the habitat instead of Arco. In 0.99b I've changed this so that Raisu gives you Arco as a target if you have the targeting ROM.