...talk about taking something out of context.
So it says that the Mardook created the Zentradi. I make pizza's for myself, will you claim that because of that, i make all the pizza in the world, Duke?
What Kaiba has been saying has been speculation based on the available facts, which include such statements from the creators as "The Mardook created the Zentradi", and "Mardook technology bare's a marked Zentradi design", and the topper "The Mardook have a fully functional, working Fleet Base". These points alone suggest a very high probability of the Mardook being the descendants of, or even the Protoculture themselves (Atleast, in Ingues' case).
...But thats an opinion based on the available facts.
Just like its an opinion that no matter how much they want to dismiss it, Macross II seems to be right in there with every other Macross works...even having its own page on the official site, and its Mecha (Specifically the Metal Siren) having an official designation.
Maybe if this speculative discussion is rubbing you the wrong way, you shouldn't continue voicing your 'obviously' non-importent opinion in it.