Just for improve the above solution posted by Flaming Jammers.
Big thanks to spanishwarrior for help!
When you reach level 4 on AirMech Arena, you can buy Erick at shop (cost 800 kudos). I'm using he while got the achievement, because he gives you +25% in-game xp bonus and +5% player level xp.
Select PvP then Custom match. Put all AI players on trainer difficulty, select the Dust map, because there's only 4 secondary bases to capture.On the countdown start of the match, buy the first level upgrade, build 2 moneymakers (cost 1.400 each) and put on sockets on your base. Don't buy the Leveler unit and if your AI teammates put this unit on the socket base, sell this immediately. Then build 5 jokers (cost 1.700 each) send they to capture the first neutral base and go with your Mech to help. Keep pressing
to build more 5 jokers.
As soon you capture this base, buy the second level upgrade, now send your jokers to capture another neutral base. Remember to keep building more jokers.
The AI enemy Mechs, will trying to capture this base, hold on and build 2 or 3 Patches (cost 2.200 each) and do your best to kill the enemy Mech.
The best tactics to to kill AI Mechs, is keep flying and hold
to fire and leave your jokers do the hard part. When the AI Mech try to fly you will kill him very easily.
As soon is available buy the Afterburner upgrade, this will make you fly faster. Build more 5 jokers and when you have at least 10, send they to capture the next base, go help them and build more jokers and patchers.
When available, buy the last level upgrade and another Afterburner upgrade. Send all your units to capture the last secondary base. When you have the control of this base, build more jokers and send all your units to attack the enemy main base. Go behind the enemy base and shoot down their generator, doing this you earn you more level points. Keep building more jokers and send they to the enemy base.
Keep firing and when you destroy the enemy base you will win the match and probably the achievement.
I got the achievement yesterday, but I still did a video to show what it looks like.
In the video I'm at level 8 while all the AI Mech are on level 4-5.