This is 20% less than you get for a solo queue victory in the pug bracket. Part of the change to solo queuing was so that grouping up as 3 and stomping uncoordinated misfits wouldn't be as appealing as getting 1 more person and queuing for 4s. It was a good idea, but obviously has failed given the ridiculous +100% (Compared to 2s,3s, or 4s) boost of solo queue.
This is not accurate.

First, # of marks and exp varies depending on the overall rank of the enemy team compared to yours. beating a team of players with higher ranks than yours yields more XP/marks, beating a team of lower rank players yields less. I got 92 marks for a solo queue win, so its not a 20% difference. Then later in the same paragraph you say its suddenly 100% more instead of 20% more? I don't understand.

Now, I agree that 4s premade should give the most reward. I'm just saying your statements aren't completely accurate.