Board Thread:Questions and Answers/@comment-31725345-20170716102432/@comment-78.194.252.210-20170717103447

Technically you are mid-right. In term of raw prana, they are more powerful because Gaia and/or Alaya give them prana. But in term of abilities and powers, servants and CG are equals. I would say more, the servant system is all based upon Counter Guardians:

"It takes 7 Counter Guardians to control the Primate Murder and the Servants of the Grail War are based on these."

Also, in Heaven's Feel, Archer make his stuff as Counter Guardian during his fight with Sakura. He was qualified as different, as if Rin did not supply him anymore, and with much more prana in him. And died against her. In the end, the only difference between them is that the Counter Force contains some monsters like Archetype Earth (Arcueid) and Primate Murder, but they are rare.

Heroic Spirits, however,  and Grand Servants, are different. Grand Servants are servants supplied by Gaia/Alaya, and without the grail's restrictions. So they can use 100% of their classes. Heroic Spirit are stated themselves as the most powerfuls existence that even magicians couldn't make a contract with (even so they can do it with gods). Both doesn't have to bother about prana anymore, and their raw powers are more than enough to wipe out the world.