Deploy the wall!
Jack Kirby's books were retconned to not actually be very official I believe. He probably took a lot more from the wider Macross franchise than the TV guys ever did.
Well, sounds like they've retconned that the Zentraedi sort of faded away, but it really is just to justify how they magically vanish after episode 36. Even a warlike militaristic culture is plenty of "culture" even if they don't know about singing, swimsuit competitions and soda. So I find the idea that they just blended into nothingness because they "lacked culture" to be more of an apologist thing for the cracks in the series than anything else. After all, they did have huge fleets of very distinctive spacecraft, thousands of years worth of tradition and technology. Where did that all go? We're supposed to believe that tech that humans cobbled together in a decade from one single crashed alien ship out-competed every single alien-designed war machine from a 500,000 year old spacefaring race, basically overnight. After all, the series makes the point more than once that humans know literally jack shit about space warfare, yet our earth-based designs cobbled together overnight just happen to trump literally every device created by a race that had been fighting space wars for 500 millennia.
... the uh, thing you seem to be missing, is that the zentraedi knew roughly jack shit about the stuff they were using. Basically everything that
wasn't combat was handled by the masters (with rare exception ala Exedore, and even his shtick was mostly that he was a once-in-a-generation genius), right up to and including basic ship maintenance (it's actually a plot point somewhere or another, with zentraedi ships having mechanical difficulties due to degradation because their crew had no sodding clue about what basically anything did or how to fix it when it broke). The zentraedi were not a race that stood on their own -- they were warlike and militaristic, but they were also a
slave race, literally created to serve another one, and intentionally kept in technological ignorance and away from cultural influences to make control an easier thing.* That's why the culture thing happened like it did, with the humans managing to get communication going on with the zentraedi when they were far away from the Masters' influence and on a mission that wasn't explicit genocide (which was mostly how they avoided the problem before that point -- the masters just gave their soldiers orders to murder pretty much absolutely everything that tried to talk to them). It's also why there just wasn't much zentraedi culture
to overwrite. Basically the closest thing they had to that was some engineered in aggression, with almost everything else being "Obey the Robot Masters". They had combat and some industrial (mostly focused around extraction) skills (and that wasn't the terribly impressive; most of it was just due to their size) and... pretty much nothing else.
And... yeah, you actually seem to have no idea what the SDF
is. The humans didn't cobble together something that happened to trump every device created by a race that had been waging galactic wars of genocide for millennium, they took the mostly intact masterpiece culmination of technology that said race's more or less most brilliant scientist
ever made, that had a working mcguffin device that could power literal galactic empires, and then got it moving again. That's the SDF 1;
Zor made that thing, it was barely damaged by its crash (or at least the important parts were), and it took humans decades of freakish magic space plant/energy exposure on top of a few ridiculously capable experts (and Zor clones, don't forget the Zor clones) to even
start to understand the thing, though they at least got it working (mostly) before that point. And all that on top of the zentraedi not really knowing how to use a lot of their material -- it's (or at least was) canon that the post-war human/zentraedi organization managed to get some of the remains of the initial fleet to work several times more effectively than the zentraedi alone did; the Factory Satellite being a primary example of that. The humans have a hell of a time when they run into the actual Robot Masters, and a large chunk of the reason they didn't get just straight up exterminated at that point was because the RMs were facing a seriously major energy crisis, on top of a fair glob of other stuff. They got their asses kicked to a fair extent even with a number of years of extended R&D supplemented by what the zentraedi was able to help with and what amounted to a protoculture rosetta stone (in the form the SDF); just about the only reason the first war didn't end with no more humans was because the RMs
weren't there, and were stingy about their technology when it came to independent zentraedi forces (and even then, the zens actually
did have mechs that strictly outperformed the veritech and battroid stuff, with the female elites being an example). Plus the zentraedi, like the RMs themselves, were fairly badly energy starved at that point.
I'd probably guess part of the problem you're having comparing the tech is that most of the screen-time stuff we have (even with the supplementary stuff) is focused on ace pilots, many of them basically inhumanly (sometimes literally, sometimes
very literally once protoculture shenanigans really start kicking in) skilled. The veritech stuff helped a bit with unexpected movement and whatnot, but to a large extent even with that most of the time the RDF forces barely held on, if at all. It took a
lot of things going the humans' way to make robotech happen, from a canon perspective (and do remember, they still lost >70% of the human population and the Earth ended up with ~95% of the surface hit with orbital bombardment). There wasn't actually many instances of technological parity except when the SDF got involved... and again, the humans didn't make that. Just incredibly skilled pilots that happened to have tech that let them leverage that abnormally well and said oversized mcguffin mcguffin carrier.
... though yeah, as per furt, the supplementary material outside the actual TV series really did a hell of a good job of making sense of the series itself. The books were the big one, but even other stuff (comics, games, etc.) helped a fair bit, too.
*And if you think that's stupid, you wouldn't entirely be wrong. Iirc there were protoculture exposure issues among other things that had been screwing with the RMs' minds for a long, long time. They were basically brilliant with incredibly bloody impressive technology, but also effectively brain damaged and acting fairly erratically because of it, on top of just kinda' being colossal jackasses to begin with.
