I'm not fully sure Jalter can pull from that wide a range. It was pretty well specified that the only two things in the Grail were her and Vlad. If Jalter starts pulling Medb's power, she's not pulling from the Grail, she's straight-up jacking the Throne. So it's pretty much the Servants that were summoned for this war, maybe even just the ones still alive.
Pretty much this. My thinking, Doylistically speaking, was 'hey cool I can jigsaw together most of Jalter's canon powers from bits and pieces of already-summoned Servants, neat'.
However, I have of course prepared an explanation/excuse/handwave! Any Servant killed before Jeanne was already fully converted into magical energy by a properly-functioning Fuyuki Grail, so no abilities from those. Jeanne was busy trying to resurrect when Gilles died, so didn't manage to filter anything from him either. Vlad was around and actually semi-conscious for the intervening sixty years, not that Jeanne knew that, so his Noble Phantasm was available for her to base La Grondement du Haine off.
Of the Fourth War Servants… well, surprisingly few give her any kind of upgrade given that she's already in Due's overpowered body with overpowered stats that she can tweak at will. A lot of what they do is based on technical skill and experience rather than just having superpowers (Archer, Saber and Caster are all this type), which Jeanne can't just integrate. Berserker's flames are pretty easy to use, and you know that Jalter would have gone for that over Disengage. Rider's prayers and Miracle are off the table for obvious reasons.
So, yes, for all intents and purposes this is 'canon Jalter with canon Jalter powers, except played by Enkidu'. I guess that wasn't especially clear, was it? This is what I get for trying to half-assedly add in things I think are neat, I suppose…
