Some food for thought:
Q1: Which mission gets you more credits?
A: Of course the support XP gives twice as much!
Q2: Which mission is harder to do?
A: Well, it is a little more complicated, but let's get to it.
Arming secondary objective: 100 obj. XP
One fully charged revive: 100 sup. XP
2x direct hit with ammo pack: 100 sup. XP.
Arm C4 on primary objective: 200 obj. XP
Long defense bonus: 200 obj. XP
Having ammo station deployed at spawn point: 200 sup. XP each spawn wave if 5 teammates spawn
Destroy secondary objective: 300 obj. XP
Spot 5 enemies with Redeye: 300 sup. XP, +500 if they die while spotted (800 total)
Destroy/deliver primary objective: 1000 obj. XP
Friendly Rhino camping your health station for 1 minute: 1000 sup. XP + whatever health insurance bonus you get
Also, the only reliable way to get objective XP is escorting/damaging the EV, and long defense bonus (team selection is random though) If you are in the attacking team, your teammates arm C4 on everything before you get there and you lose the match, you get little to no objective XP (only source is "guarding" the objective)
Even better, if the enemy team is much better and your team gets spawncamped, you can still drop ammo/medkits for yor teammates and revive them, but you won't get any objective XP
TLDR: in general support XP is much easier to get, because it is tied to using abilities on teammates, which is more safe than trying to destroy/deliver the stuff the whole enemy team is trying to defend.
I think 2500, 3500 and 4500 for objective XP, and something like 4-5-6k for support XP for the 500C 750C and 1000C missions would be more fair.