I think more important than matchmaking is the mission design.
It is completly unbalanced.
There are spots that are too easy to defend because of the spawns or what ever.
The other problem is the reward system, there is almost no difference in winning 5 stages and the last one, or only the last one.
Also when you win 5 stages but lose the last one you get not enough exp/money for it.
Then there is also a big gap between mission if you count the exp/money per minute.
Losing missions fast, give more exp/money than winning missions that take 20min+ because of the long stages