So is that the actual Heroic Spirits, or the specific Servants that appear?
Because we have several Servants of the same Heroic Spirit if we include stuff like Grand Order and such (Saber, Saber Alter, Saber Lily, Arturia Lancer etc).
Also, what about their prana sources? Are they fully reincranated, and thus able to use all of their abilities to their fullest?
If they are indeed the Heroic Spirits instead of Servants, does that mean that various abilities and NP's work as they should, rather than as their limited version (due to having to manifest inside a Servant container)?
I am thinking here very specificaly about Karna and his armor, which in case he is a Heroic Spirit should give him a full, 100% resistance to pretty much anything, making utterly immortal and invincible, but Siegfried's and Achilles's immunities to damage should also benefit from this, for instance.
A full-powered Karna without any real limits on his prana supply
can fight Gilgamesh on an even footing, for instance.
This is all of course ignoring stuff like Solomon from Fate/Grand Order, with his EX Everything