Its honestly not that hard if you know what to do; I developed a very solid strategy to get to wave 5 consistently:
: immediately walk up and go into action response mode and use your machine gun on the viper until you almost run out of time (you never want to run your gauge empty). Then walk back and he should rush you...hit
to knock him down and put half a clip of your machine gun into him and hit reload, jump back and go into action mode again..lay down fire on viper until your gauge almost runs out again. He should be almost dead now. when he charges again hit
and repeat the above process. DO NOT PICK UP THE UPGRADE HE DROPS Then finish off all the little guys with your assault rifle.
go to the center circle area with the statue and throw a grenade where the bogey comes out, you must time it right but it will knock 1/4 of his health off. He should get knocked to the side and you should activate your action response mode and lay as much machine gun fire into him as you can (you should have around 100 shots left after the viper in round 1, but do not pick up any more machine gun ammo). Exit the mode when your gauge is almost empty and boost dodge around behind the statue until both sets of flying bots spawn. Throw an EMP and this should kill all the flyers. Now boost dodge around until you get good position to take shots on bogey and enter AR mode to lay into him with the machine gun until he is dead. Before you finish off the smaller guys make sure you have a disk launcher, LFE gun, and assault rifle for next round.
From where you spawn there is some cover that goes up the stairs to the right behind some rubble...go there. when the spawns come throw a grenade where the 5 infantry RI come from and blow them up. When the bigger fellas start spawning in, first enter AR mode and shoot a disk launcher at the rocket launcher RI and immediately go behind the cover. Come out almost just as fast and enter AR mode and shoot the flamethrower RI in the gas tank with your assault rifle until it explodes. Go back into cover. Come right back out with your disk launcher in AR mode and shoot the disk at each of the big RI's heads. You should now have all them decapitated and they will wander around and shoot aimlessly and in random directions. Just stay in cover and they will eventually fall over and die from having no head. BEFORE the next round starts make sure you have EMP grenades full, assault rifle, LFE gun, AND THE ROCKET LAUNCHER one of the larger RI drops.
Stay near the cover from the previous wave and when the spawns are about half way in throw and EMP to the spawns near the statue. Turn around and enter AR mode before the blue flying RI spawn and when the spawn shoot a rocket at their feet to destroy all four of them. Immediately slide to where you threw the EMP and use the next rocket to take out the other set of blue flyers while they are EMP'ed. boost dodge back a bit and shoot one shot of your LFE at the sphere RI's (one shot with the LFE on the spheres will kill them). By the time the flying turret should be comming up from the right side behind the cliff...take your rocket launcher out and fire your last shot at him. Boost dodge and use the LFE to take out the remaining spheres and then go into AR mode and eliminate the last flying turret with your assault rifle. Now you can relax. Go get the upgrade from round one for your rocket launcher to replenish your ammo. Refill your LFE to max with the second LFE. Now just boost dodge around and take your time eliminating the scorpion RI's with your assault rifle. Before you kill the last one, you should have for the next round a couple EMPs, rocket launcher full, full LFE, and a full machine gun.
Again start near the cover mentioned in wave 3. When the spawns come in throw and EMP to the point up the stairs where you start the challenge. Then go into AR mode to take out the 3 spheres that spawn in front of you with one LFE shot. Boost dodge to the EMP'ed spheres and hit them with one LFE shot. Boost dodge around and eliminate the three remaining spheres with your LFE. All that should be left is the bogeys now. Pull out your rocket launcher and keep boost dodging around until you get an opportunity to go into AR mode and fire a rocket at one of them. Whichever one you pick...stay with that one...it is important to take one out as fast as possible. Make sure you boost dodge away anytime they throw the weapons that overheat your suit....if you get overheated you are likely screwed but throwing your last EMP should save you once. Boost dodge around and land 3 rockets on the same bogey. Exchange your rocket launcher and get the lock-on-laser. Boost dodge around and use it only in AR mode on the same bogey. You should be able to take him out this way. Once you get the first one down...it is simple...take your time...boost dodge around enter AR mode and hit him with the lock-on or machine gun