I don't see how Palmer's season can be considered anything other than terrible so far. In qualifying Magnussen is ahead 5-1 with a median gap of 0.276% and a mean gap of 0.298%. For comparison over their time together Hamilton beat Button by a median of 0.272% and Vettel also beat Webber by the exact same margin of 0.272%.
In races it is 2-2 which looks quite even, but if you were to compare points tallies it would not, even the official tally of 6-0 is deceptive.
I've been using an alternate system where positions outside the top 10 are awarded fractional points to allow me to separate drivers in poor cars; 11th is given 25/50 = 0.50 points, 12th is given 18/50 = 0.36 points, 13th is given 15/50 = 0.30 points and so on. Non-finishes are not awarded any points nor are positions 21 and 22.
With this system Palmer has scored 1.10 points to Magnussen's 7.18 - meaning Palmer has only scored 15% of Magnussen's points. Palmer has suffered a mechanical DNF though so if we judge them by points per race instead then Palmer has scored 18% of Magnussen's points, which is a little better but still awful.
The only more one-sided team mate comparisons are Verstappen-Kvyat at Toro Rosso (12%)* and Gutierrez-Grosjean at Haas (6%).
*Verstappen and Kvyat have not been team mates of course but I can still compare their scoring rates in the races they did do in the team, but since that sample is just 2 races so far for Kvyat I don't give it much consideration. At Red Bull Kvyat's points per race tally is 57% of Verstappen's but that still has the 2 race problem.
I expected Palmer to be poor but his performances have even surprised me. It's no wonder that his seat is constantly talked about being under threat.