Fine, if that's the kind of nitpicking you want to bring aboard then why not. I appreciate the quotes there though and see where you come from, and I have to say I agree with you regarding the WINNING the argument thing.
From my point of view, the whole Bosch arc story is a tragedy. It is "Exodus denied" so to speak. Thematically, it fits together with the rest of FreeSpace 2 as another failure to bridge the gap between us and the shivans. I do think there is truth in both claims that we are incapable of communicating the shivans and that this attempt was almost successful. The point is, thematically, it failed. How can I speak of it as a "failure"? I agree with you here that I might be too quick to judge on what happened to Bosch and whatnot, there is a glimmer of "open question", mythical even, to what happened to him. Plotwise, he could have gone and continued his mission to build some arrangement with the shivans or anything else. Thing is, we are blocked from knowing anything like this. The shivans remain a muted species by the end of the game. To us. And narratively, any other end of this arc wouldn't work. This has been built up on and on from the very first chapter, and the conclusion couldn't just be a dead Iceni with the captain at the helm without his head or whatever. It wouldn't work because why then even bother to rendezvous? Just beam them out of the sky.
It also works within the scope of the player. You want to know what happened. You want to chase Bosch. But you can't, because a new Sathanas is just about to beamraep your vasudan destroyer and the whole tone changes. Again, shivans deny you from one more thing. This begins a series of disappointments and the retreat of expectations and ambitions. Bosch touched the gods of the galaxy at the very peak of human ambitions (they had defeated the NTF and were about to just conquer everything shivan related), and right at that very moment, everything recedes and you are ultimately denied of any truth, any power, any conversation.
I see the whole work thematically, and it all boils down to several NOPES. I said this already. Again, these NOPES start to become real game changers by the time Bosch is captured. NOPE, you don't get to know what happens to Bosch. NOPE, shivans won't communicate anything to you or any other human again. NOPE, you don't get to know shivantown. NOPE, you are not as powerful as you thought at all. NOPE, we are not going to steamroll you, it's not even on our radar. NOPE you won't get an explanation for what happened. And this tone arc couldn't be more strident: the game starts with the "New Alliance" ambition "to guard the tomb of space, and to find within its cold expanse the salvation of our race" and it ends after this terrifying sequence of NOPES with the only upside of the hope to get back to Sol, like a wounded humilliated kid limping, trying to find his mommy.
This is not a story about a species that is about to recover and "try again!" against the "cold expanse" after Capella. This is why I characterize the shivans the way I do, regardless of your interpretation of Bosch's arc. (I have no problems with your version too)
Metanarratively, this could just as well be designed in a kind of "Empire Strikes Back" manner and the end of FS2 just a damn good cliffhanger, with Bosch's arc to be finished later. The point of bringing that quote from the writer was to somehow ground good skepticism on this angle of attack, not to bring anything "outside" as a cheat, etc.