I should preface this by saying that I did not do a "careful, thorough, thoughtful read of Gutierrez from cover-to-cover." :) Thoughtful, perhaps, but there were boring bits (probably those very orthodox arguments you mention) I just skimmed over. My purpose in reading wasn't to understand every nuance of his argumentation but rather just to give me a better sense of what had inspired later works and to look for particular nuggets of wisdom I found interesting/inspiring/challenging.
I don't read the passage about theology and action the same way you do - I don't think he's saying theology should precede action. If anything the language of "accompany" and "linked to" suggests (an ideal?) that they develop side by side. But, yes, it is clear from the book that liberation theology is already a thing and that the purpose of the book is not to "create" it but to systematize the arguments for it.
I'm not really familiar with secular theology beyond Bishop Spong, who I find interesting but is not the approach I resonate with most. I think there's something to be said for your argument that secular theology basically leads to a non-religious/non-theological culture but I think Spong would probably respond with something like: If so, so what? In his view there is no other option that has full integrity so if that's the inevitable result, so be it. I think Gutierrez's arguments are of a slightly different vein and actually does a pretty good job of arguing faith isn't secondary or marginal - that action without faith or that marginalizes faith is in danger of going off the tracks and, at worst, is outright dangerous. I can't speak to whether his arguments have veracity beyond saying that for me personally liberation theology one of the few things that has kept me within the fold of organized religion. And, yes, there is a certain irony in an agnostic Christian saying secular theology is a problem because it undermines faith, and probably also a certain irony in agnostic Christians debating the finer points of theology. :D