With the Cyborg-spawn covered, the entire rest of Nexus' ground forces are 2 more cyborgs just west of point 3, and the "you don't want to fight this" force in the SE corner. This general lack of groundtroops is why I say you don't need more of your own.
Move your battlegroup SW and up onto the cliff at point 3, removing the SAMs, and replace them with your own structures.
During their call for help, Alpha wans AA units. We'll do one better; we're gonna turn this stage into a deathtrap for planes.
This whole time, NEXUS aircraft are going to be attacking you. don't hesitate to send damaged units to the nearest Repair Bay (likely the one at #2), as the NEXUS rocket-planes will keep going after the same tank until it dies; if that tank happens to be behind walls of AA... NEXUS won't get to it.
Move your battlgeroup just east of #3, looking for the last 2 cyborgs; once dealt with, move them to the end of the green arrow, and let them sit there while your trucks move on to point #4, and set up to prevent any more VTOLs from annoying you.
The AA pits in the far bottom corner will get hit by bombers; keep a truck nearby to replace lost AA pits.
Once point 4 is covered, send a single tank (Assault Gun) up the cliff at 5 to shoot the trees and then BACK UP, and send in the trucks to build defenses up here, and then BACK UP.
The lines in the last screenshot indicate how far you can move forward without "spotting" the Alpha team. The instant you see any of their units, they go "live" and the NEXUS force in the SE corner mobilizes to intercept them.
We don't want that happening until our full defenses are up.
When all is set up, save the game before performing the rescue.
You will notice that all of the alpha units (sans the trucks and repairtanks) are HERO level. By this point, you *might* have a single hero unit, and that being your commander. We have the chance here to pick up a lot of ubertanks, and we don't want to miss the opportunity.
When ready, move a truck to "spot" team Alpha, and then immediately move Team Alpha behind your defenses.
The trick here is that Alpha had "walled themselves in" to their valley, effectively bottlenecking their own retreat.
AS SOON AS you gain control of them, have their trucks demolish all of their "wall", so that they can get out ASAP.
When NEXUS attacks them, the Hero tanks "should" have enough time to get behind your defensive wall. The repairtanks and trucks will drop like flies, but we don't care about them.
If you notice you lost a Hero unit, reload the game and try again.
If you try to save them multiple times and simply can't, consider sending in your 6 Tiger-Tank battlegroup to "screen" the ramp and take the shots. If you are going to have to lose tanks, may as well be the unexperienced ones.
But that shouldn't be necessary. Only if a Team-Alpha Tank comes under directed focus fire will it's Python-body Hero-level self be lost.
Once you get behind the defensive wall, NEXUS will "stall" on the defenses while you retreat your force back to the landing zone. There should be no NEXUS units behind you, so the Yellow retreat routes will be faster than trying to backtrack the Green one.
Get to the LZ (don't forget to pull back any trucks you have on Repair duty at points 4 and 2), and the stage will end.
SAVE YOUR GAME. I'm sure you've been saving your game after the end of each stage, but due to the way Gamma 5 works, you will want your "successful Gamma4 Completion save" to be it's own slot.
There is a bug in version 2.2 of the game (not sure if it's still around in 2.3, but I'll mention it here just to be safe) where if you recycle a unit, save the game, quit the game, reload the game, and THEN try and build something, the recycled experience is LOST. And Since we will be recycling stuff in Gamma5 and not rebuilding it till Gamma6, this is huge.
END GAMMA 4