HUH??? Bruce took Dick in when he was a little boy (when he most certainly did need a father) and raised him, fulfilling the role of father in every way. The fact that he didn't call him a son, partly due to him not seeing himself as a father and partly due to Dick having a father who died (also very much due to conventions in 1940, though even there Bruce described Dick as "like a son to me"), does not change that they are father and son. That's why the adoption of Dick was emotional, because they were saying what they had both already felt for years.
The words that weren't said between them (father/son) have been a big thing in their relationship for years. Like at the emotional climax of the Prodigal arc. And even before that Dick naturally contrasted Bruce and his own father (who's only a memory). Part of the reason Bruce didn't call him a son was his absolute dread of that bond. It's scary having a son.
That's even gotten amped up with the "death" of Bruce--Alfred coming out and saying Bruce was his son, three sons battling over their father's legacy. Every other book in the line is playing a family mourning drama imo.
By no means does that undermine their connection or obvious love for each other, but to me it does put it in a slightly different category than strictly father/son in the traditional sense.
I think it does undermine their connection and obvious love for each other to suggest all those emotional moments around the words father and son, and even the legal adoption, doesn't make them father and son compared to a blood relationship, even between strangers. They're not a traditional father and son any more than Bruce and Alfred are a traditional father and son. Their family is non-traditional. I don't think Dick would ever want to encourage Damian in his selfish and sometimes childishly cruel demand to be seen as Bruce's only son. Dick might not be insecure about it since he already went through years of angst over this very issue, but Tim's going through his own version right now.
Of course, it's entirely possible that I'm wrong about the authorial motivations that factor into the story, and if that's the case I'll happily eat my words in another issue or two. :D
Based on what I've read in interviews that are then repeated in the books I feel like GM isn't hiding this intention at all. It's not, it seems to me, that he's trying to diss the other boys, just that he sees Damian as Bruce's first son and assumes everyone else would see it the same way. I would love it if it turned out that this is the beginning of an arc where Damian comes to see that Dick and the others are Bruce's sons and his brothers. If that happens I'll definitely appreciate it.