You can best view them as -ms vs -me. Two different sets of macros to markup the text with semantic information that's then turned into useful rendering by a variety of ways. texinfo and latex are completely unrelated at a code level. LaTeX predates texinfo by some time (I've not looked it up, but I encountered LaTeX years before texinfo, though it's possible I just ignored it when working on bringing up GNU Emacs on VMS 5.mumble back in the day). It was always my impression that texinfo came more from the ITS info file world and that the TeX bits were initially just a hack because it was also on those machines... It would be interesting to hear from people that were there.
That was always my impression. Stallman hated troff (and man) because it was not integrated into EMACS (his operating system). I always got the impression that texinfo was more of a shot against man pages and trying to push the purity of the 'ITS-way' to Unix. And of course the problem became the more he did that, the less use texinfo became except for anyone that followed his gospel. As Unix became the mainstream, it meant information for any gnu tools was (is) disjoint. If rms had been willing to just accept the man command itself, I suspect that would not have been.
To be fair, its not an unusual behavior. Folks coming from VMS (or windows) try to make Unix look like that. And what did we do with VMS, we added the cshell and Unix tools so people like me could type on it. I'm currently being driven nuts by the simh tool which has a very TOPS/VMS style feel. Everything is help commands. The documents are quite sparse. To me the documents/book (or man pages) should primarily ' go to' and if you want something like 'help' then create it from the documents. But I can not really complain. It's a wonderful tool and its author comes from that heritage not Unix. The problem I remind him is that he will get silly questions from people like me, because we can not find things in his help system - its just not how a Unix program tends to work [I want to look in the index of the document, and find the section myself].