The interesting thing about Delta is that, thus far, the stakes have been actually quite minor.
The Kingdom of the Wing has been objectively the weakest "villain" antagonist yet seen. Zentradi, Protodevlin, Vajra, all were orders of magnitude more dangerous to human life and liberty than the Windemerians. Their standing military is shown to be a single Protoculture battleship and several wings of highly skilled and technologically advanced fighters. A single pilot might down 20 VFs, but for each loss they'd take it would be unsustainable.
They have no invasion troops, no reserves, and their backup forces are limited to whatever they can subvert via the Song of the Wind. Even WITH the Protoculture ruins so far, their influence is limited to the far frontier of NUNS territory. Because of their insistence they are "better" than their enemies, they've thus far caused no extreme damage to conquered planets. That's not to say they aren't responsible for many civilian deaths, they are, but they thus far haven't resorted to orbital bombardment or concentration camps or the like.
Interestingly, their whole strategy has hinged on "culture shock" and should that fail, they have absolutely no recourse. Their society seems fairly unadvanced prior to being uplifted, and should their corporate backing fail, they'd be in even worse shape. One battle with a Macross class ship nearly crippled their whole scheme. Against a more formidable force? They wouldn't have had a prayer.
This doesn't make the battles any less exciting or the stakes worse for our main characters, but it's interesting that this is one of the lowest intensity conflicts we've seen yet. All of their Var infected support base could (and most certainly will when Walkure recovers) disintegrate before their eyes.
Simply put, the Windemerians are children lashing out at the big boys, and what seems to be clear from their wounded pride is that they know it. They're also terrible strategists driven in part by their impatience, and all of their short term gains can just as swiftly be rolled back. They also haven't demonstrated any of the inspiration or improvisation the SDF-1 did when it was fighting similar lopsided odds, and have no reaction weaponry. It's either SONG OF THE WIND, or nothing. Simply put, I think they're going to run out of steam fairly quickly.