You don't see many enemies with more than 50 ESP, but many areas have enemies with well over 35 ESP that you want to paralyze. In order to achieve 100% activation rate, you need V501/2 and the android bonus in ultimate against enemies with 30 or less ESP with a Spread Needle. For Arrest, you need enough ATA to hit (which you get plenty of on the third attack of a combo, which already has almost universally has 100% hit rate, and against frozen groups of enemies on the second or third attack with RAcast/RAcaseal freeze traps you are guaranteed to hit). Spread Needle with ~50% Hit can also achieve this without the freeze trap, and that is the advantage of it. However, against anything with more than 30 ESP, the Arrest Needle is better.
Long Story short: Against weak enemies, Spread Needle is better (less than 30 ESP) on androids. Against all enemies, Arrest Needle is better on fleshies. Against strong enemies, Arrest Needle is better (more than 30 ESP) on androids.
Most groups of enemies involve at least one type of enemy with over 30 ESP (usually around 35-45 ESP) and you cannot achieve 100% activation against them with a Spread Needle although the ATA on it will connect every time due to its Hit%. The Arrest Needle, on the other hand, achieves 100% activation on damn near every enemy in Episode I and its accuracy "problem" is *more* than augmented by the Freeze Trap's massive EVP reduction. The S-Rank Needle is better because it can make up for its weakness with something as simple as laying a freeze trap.
Spread Needle, on the other hand, can't even achieve 100% activation against the wolves in Forest 1. (64 + 30 - 35) x 1.5 = 88% paralysis chance against wolf
While an Arrest Needle has enough activation to handle anything up to and including the later stuff in Desert. Its activation rate is 100% on EVERY DAMN ENEMY EXCEPT THE MERISSAS. 100% means it does not fail to activate. No enemy (except Del Rappy) has enough EVP to dodge an s-rank needle attack while frozen. They will get paralyzed.
With an S-Rank Arrest Needle, you get:
(80 + 30 - 21) x 1.5 = 100% paralysis chance on Goran
(80 + 30 - 32) x 1.5 = 100% paralysis chance on Pyro Goran
(80 + 30 - 36) x 1.5 = 100% paralysis chance on Goran Detonator
(80 + 30 - 41) x 1.5 = 100% paralysis chance on Girtablulu
(80 + 30 - 45) x 1.5 = 100% paralysis chance on Sand Rappy
(80 + 30 - 58) x 1.5 = 78% paralysis chance against Merissa A, hardest thing to paralyze in EpIV
compared to Spread Needle's ****:
(64 + 30 - 21) x 1.5 = 100% paralysis chance on Goran (don't get used to it)
(64 + 30 - 32) x 1.5 = 93% paralysis chance on Pyro Goran
(64 + 30 - 36) x 1.5 = 87% paralysis chance on Goran Detonator
(64 + 30 - 41) x 1.5 = 79% paralysis chance on Girtablulu
(64 + 30 - 45) x 1.5 = 73% paralysis chance on Sand Rappy (...)
(64 + 30 - 58) x 1.5 = 54% paralysis chance on Merissa A
Conclusion: Spread Needle sucks.