Sounds interesting.
Though I agree with you, you fight, then buy a box, fight and vice versa. My suggestion is: We can have some sort of events every special occasions. e.g, Easter Event at April.
How? Every 5 win streak, you will get the so-called "Easter Mech Egg". What is Easter Mech Egg? You can open it, and you'll get random items mythical items, legendary etc. However, mythical's percentage would be as low as 0.5% For other items? The percentages are a bit higher. However, legendaries- 8% Epic Items: 28% Rare: 45% (Note: Rare items percentage would be lower than the original.) By the way, Easter Mech Egg gives you 5 items.
For Christmas:
You will receive a key. Key that would be used for opening a special, locked gift. (literally a gift) And it's called as "Intergalactic gift of Liran"
LIKE THIS:
However, in order to get a gift, you have to get a 7 win streak. To get a key, you will obtain one in after you buy 10 boxes.
Simple right? And fun!
NOTE: Easter Mech Eggs still can get you a bunch of kits. However the Intergalactic gift of Liran wouldn't get you a kit.
Here are the stats of the IGOL (Intergalactic gift of Liran)
0.9%- Mythical
13%- Legendary
30%- Epic
39%- Rare
NOTE: Those events would run for only 3 days.