This map is very soloable with Haigen+lightning, you just have to stick nearl the left hand corner and be vigilent to make sure that nothing serious gets passed the bend, then clean up anything that made it near the core on the second level.

Actually, this map is very unbalanced since the first changes made, in the early versions. It it actually makeable solo without DLC equipment - yet it is true, that this one is considered the hardest, because to win you need to go and make sacrifices on core health on purpose, knowing one might get below 1000 health, while the other stays above.

This map demands pure Hybrid Thinking and fast action jumping all thorough. One Core protected by towers while the other by the player at any time.

This map gave me serious headaches, it was undoubtedly the hardest after Roadworks to solo.

To be honest I probably wouldn't be able to finish it alone even with this maze without the Drone Launcher; even with that weapon I'd end up using way too much time dealing with the Armored Heavies on the lower grid and I barely managed to kill the Hoverer Queen on the last wave and she did land a few hits on the core.

The killzone was set on the upper core's longest tower base line with Scatter Lasers and Slow Field Dispensers, it did kill everything but a single Walker that got through somehow and, of course, the Hoverer Queen.

I've tried two killzones, one on each core, and it just doesn't work very well (and that without any Feats of Strength), one or two lumes always seems to get through whenever I do that.

Without the DLC equipment I can't see a way to solo this. Or maybe I just really suck.

Do you mean that you can't solo it on normal or with Feats of Strength?
On normal I went SiMo with Electricity offwep,
perks; marksman, hollowpoint, exposure rounds,
towers: Cannon, Lightning, Scatter, Gatling
Then I set up directly right of the initial spawn, with all my towers there for the first 5 rounds, just positioning blockers to channel them in. After that I used my extras to maze everywhere (starting with the third spawn) and basically defended 3rd on my own with 1 cannon and 3 gatling, later on 1 lightning as well, but only 3 or so got through.
The heavy boss is fairly easy since he takes a while to get there, but thats likely the hardest level. The queen hoverer just died to weakspot sniping like anything else large. Just don't skimp on lightning for the Walker Warriors or Gatling for the Walker Pups/Soakers and you'll be fine.

I'm currently lvl 20, with DLCs, I can hold on untill all 3 spawns are active...

It is possible to do it solo - yet after the patches and so on, it is recommended to have either all DLCs or a squad like you said with 3-4 players. Of course it helps a lot if you have unlocked all towers, perks and weapons as well!

You definetly need 4 players here, cant solo/duo...