Hmm. In which ways is the missile better than a starship?
- It can kill fixed targets with one shot. A starship typically has to loiter for a while to achieve the same.
- It can operate without a crew. Some users may consider crews expensive, one way or another. Most starships flying without a crew have been passive. But e.g. the Promeheus fought pretty well with only AIs aboard.
In which ways is it worse?
- It can only ever fire this one "shot", as opposed to a starship. Starships might be significantly cheaper weapons "per pound destroyed", then.
- It needs a super-advanced computer to achieve the required mission independence. Starships even without full crew don't need this no doubt expensive piece of equipment.
The rest seems neutral. It can do warp nine like any modern ship. It seems to be difficult to destroy in flight by a single starship, being resilient to fire and capable of firing back, just like any modern ship. Dreadnought itself had a measure of long range stealth, but this was probably added by Torres, and whether Cardassia could do the same is unknown.
So it boils down to whether the cost of automation and non-reuseability is higher or lower than the cost of crew. Cardassians expended at least one of these things against a Maquis munitions dump, a seeming low-value target defended by a weak opponent. Does this mean they
a) could spare these cheap things even against soft targets, even though they could do more when needed?
b) felt the Maquis were a hard target worth a silver bullet?
c) had political reasons for not sending a crewed starship to do the job?
Only b) would make it odd that the missiles were not used against the Alpha Axis in the Dominion War. And even there a saturation attack might be too expensive. We see it takes hundreds of ships to get through planetary defenses, or those of a starbase (including a non-purpose-built one like DS9). Cardassia might prefer to build a hundred crewed ships, or 99 of those per every missile.
Usually, long range bombardment in Trek has only been a concern if stealth is included (the putative Maquis missiles of "Blaze of Glory", the long range torps of ST:ID). And Cardassia only got cloaks for the Obsidian Order from the Tal'Shiar.
Timo Saloniemi