What is this question even... Let's break this into chunks.
For starters, what exactly is the current state of gaming? You make it seem as if somehow, even though HALO wasn't anywhere close to the first FPS, that it somehow made the entire market go full FPS games only. Last I checked, most people have been praising games like Undertale, Rise of The Tomb Raider, Yokai Watch, The Witcher, Bloodborne, and countless other titles from this year alone that don't even fit that genre.
I mean, FPS games have been a big thing since the original DOOM. It's a genre that does indeed see some big advertisement and seems to have the loudest audience overall just due to the fact that one of the biggest gaming publishers in the industry likes to cram it into your face (/looks at activision,) but that doesn't mean the industry as a whole has been dominated by this genre.
What I usually think about questions like these, is the person asking is sick and tired of seeing the, "same game every year," shoved in his face, and forgets to pay attention to the other releases that surround the one that's making a whole lot of noise. When I see this argument, I typically like to refer to it as ignoring the belligerent drunken asshole at the pub, to pay attention to all your friends and some of the good looking people around you.
To answer your question specifically in terms of Did Halo start triple A FPS shooters being a thing? Maybe, I'd like to think DOOM and Wolfenstien set the precedent, Halo carried it further, than Call of Duty slowly took over into making it a multi-million dollar a year juggernaut.