Be able to pick which lvl mech you fight against. com, and player.

also, needs longer lvls. if you have shorter lvls, then it gives you less and less chances to save up to buy something because there are already new things that cost more.

last, needs more battle options like campaigns, pvc, ect. not just player vs players because there might be a high lvl mech that has weak weapons, but because of his lvl, he has to fighting against the same lvl that most likely has more abillities and weapons.

Picking you opponent has the problem that people would just pick people weaker than themselves, and that online matchmaking would take much longer, as you would have to wait for people the same level as you to be available (as you wouldn't want to fight anyone stronger, and no one weaker would want to fight you).

As for the levels, there is your experience level (xplvl, and your matchmaking level (mmlvl).
The opponents you fight depend on your mmlvl, which depends on the level of the parts on your mech (items in the shop have their level below their name, your mmlvl is show near the bottom right in the shop).

If you don't add higher items to your mech, your mmlvl wont increase.

My advice is to not upgrade your mech every xplvl. Save your money up over, say, 3 xplvls, then upgrade your entire mech in one go.