All you Needler haters have no clue what your saying once you start using needlers it makes the game a cake walk. They're the most important piece of equipment hands down swords are pointless and claws and cannons aren't as good. Why use a sword on an enemy that has 80 health and the sword does 130. When you can do 100 damage on 3 enemies with a needler.
If you have "more money than you know what to do with" anytime before 3rd generation, you've been grinding needlessly. If you've not been grinding, then the only way you can afford needlers is by not upgrading your other characters, sacrificing the usefulness of four to try to improve one. For the 20K you dropped on a Royal Needler you could have bought two Force Claws and a Cannon, allowing Wren and Mieu to kill 3 powerful enemies each round rather than allowing Ayn/Nial to kill the pointless weakling enemies on one side of the screen.
And my comment about Lashute is perfectly valid. Your opening comment was that swords are pointless, not that swords are expensive, so the fact that you get the final sword for free has no bearing on the fact that needlers do almost nothing to the enemies in the final dungeons. The low damage they do rarely makes a difference in how quickly dangerous enemies like Demonesses (Skyhaven), Wyrms (Sage Isle), or Guardians (Lashute) are killed. I assume by "Plasmid" you mean Planar equipment, and by that time yes, you have all the money you ever need and could spend that money on royal needlers instead. And not be able to kill anything that Kara isn't going to wipe out with her slicers anyways.
The only time I have ever found needlers useful is a) solo runs in generation one and parts of generation two or b) if I try to make Lena actually useful in a regular play.
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At the risk of reigniting a fire, this all comes down to numbers...
The most powerful needler (royal needler) has an attack of 44. The steel sword has an attack of 46. To compare apples to apples, the royal sword has an attack of 153. So against a single enemy the two royal needlers are just over half the attack of the royal sword.
They make sense for Lena because the strongest knife she can get is the steel knife with an attack of 20. Technically she can equip any knife but that's the strongest found in the first generation. The strongest needler she can equip is the ceramic needler with an attack of 15. Toward the end of the first generation there will be a lot of battles where she gets 4x15 attacks instead of 2x20. If the King of Cille wasn't so easy it would be a good strategy to swap her needlers for steel knives just before that fight because the first row of enemies will be gone after one round regardless.