This is how I think it should be:

1 Mark / 0 XP base reward
Win: + 60 mark / +100 XP
Each action you take grants .25 Marks/.25XP
If you kill someone you get a modifier of 1.4x on your action bonus (max 2.2)
For each 1,000 damage you get a 1.05 modifier on your action bonus (max 2.0)
For each 2,500 damage you heal you get a 1.05x modifier on your action bonus (max 2.0)

Also:
If match ends in 1:59 or less : 1x Modifier on action bonus
If match ends in 2:59 or less : .95 Modifier on action bonus
If match ends in 3:59 or less : .85 Modifier on action bonus
If match ends in 4:59 or less : .7 Modifier on action bonus
If match ends in 7:59 or less : .6 Modifier on action bonus
If match ends in 8:00 or more : .4 modifier on action bonus
Any action take after 8:00 grants 0 action bonus


This way, if you AFK you get basically nothing, and if you try to sit in the instance for too long trading blows and letting the healers heal the crap out of you, your rewards dwindle to very low amounts.

A Typical win that lasts about 2:45 with 50 actions and 2 kills, would look like this:

Base
Match Bonus:
1 | 0
Win Bonus:
60 | 100
Base Rewards:
61 | 100
Bonus
Action Bonus (50):
12.5 | 12.5
Kill Modifier (2):
1.8x
Damage Modifier (11,000):
1.55x
Match Time Modifier (2:45):
.95

Total:
85 | 123


Maybe the action bonus is a little low, but I think that for the most part this would motivate people...if you can increase your marks and xp by roughly 50% by putting effort into the battle, and if you can get 1 mark and 0 xp for taking no actions and your team losing, it would stop people from queuing up.