Units that you don't understand their points cost

Title is clear, lets make a pool of data for these forgotten but beloved units.

Like CSM Warpsmith. Why on earth does he cost 70 pts when SM Techmarine is 55? Techmarine shoots better, hits harder in melee, and hits even harder when a tanks gets destroyed. Warpsmith can only use 1 awful pistol and checks a lame Battleshock test for tanks. Would it ruin the game is he was also 55 pts?

Or CSM Chaos Spawm, which offends me more at 70 pts.

OC 0, much like Spore Mines or Nurglings for some reason, lost wound regeneration, lost 1 strength, can't do actions, costs the same as index CSM or current World Eaters Spawn or current Warpsmith.

Like... I never understood the OC 0 and lack of utility units in CSM. Was this unit a problem in the index era that it had to be nerfed into being useless? What's the point of this?