I assumed Palmer came with plenty of cash considering how loaded his father is, but regardless Maldonado also comes with a GP2 title but it hasn't prevented him from being one of the worst drivers on the grid. Unless Palmer massively over-performs relative to his junior career then he is going to be much the same as Maldonado, minus the crashes.
As for Nasr, Palmer and Nasr were in GP2 together for 3 seasons, 1 of them as actual team mates. But Palmer always had 1 extra year of GP2 experience and 4 years of extra car racing experience than Nasr did including 2 seasons of Formula 2, which is roughly equivalent to GP2, and a season of GP2 Asia. Despite this Nasr beat Palmer in 2012, as a rookie, and in 2013 as his team mate. It was only in 2014 that Palmer beat Nasr, but their differing levels of experience is not something that can just be ignored. Somewhat bizarrely if you total up both drivers' points over those 3 years they scored exactly the same amount - 473 each.
Neither Vergne or Magnussen ever entered GP2 so it's a bit unfair to hold that against them. They did both enter Formula Renault 3.5 though, which is roughly equivalent to GP2. Magnussen finished 7th in his rookie season and then won in his second. Clearly superior to Palmer (or Nasr for that matter).
Vergne made his debut in the final third of the 2010 FR 3.5 season. Despite only taking part in, well, a third of the total races he was classified 8th overall. Across the races he started Vergne actually scored the second most points of any driver, narrowly ahead of fellow rookie Ricciardo and just behind Estaban Guerrieri who was in his 11th year of car racing at the time.
Then in 2011, Vergne's first full season, he finished 2nd overall just behind the very impressive but more experienced Robert Wickens and ahead of Ricciardo (although Ricciardo missed 4 of the 17 races).
In summary:
Palmer: 28th, 19th (Asia series), 11th, 7th, 1st.
Nasr: 10th, 4th, 3rd.
Magnussen: 7th, 1st
Vergne: 8th (partial season), 2nd.