Could someone explain it to me, because it seems nothing else than a bug/overlook.

E.g. "Harpoons" research enables 3 types of missile weapons:

1. Prototype Antimatter Missile.    Requires 1 Antimatter, causes 2 Damage.
2. Harpoon.                                    Requires 1 Antimatter, causes 5 Damage.
3. Phoenix.                                     Requires no resource, causes 4 Damage.

It's obvious that the first type makes no sense. Why would anyone buy it? It is in no way better than the last two.
(It does provide higher "Threat" than the next two, but firstly I have no clue what it is and I could find it anywhere. Secondly, I doubt it's worthwhile anyway).