[1] Sure, sink or swim... but what I'm saying is that if everyone else is suddenly swimming instead of sinking, your swimming stops looking so special. Seems like a pretty simple concept to me. Halo was the first to get to a certain level of quality. That level of quality stopped being exclusive to Halo over time, allowing various other aspects to factor more heavily into which game someone chose.
[2] Everything you do in Destiny, win or lose, singleplayer, co-op or multi provides consistent reward and sense of progress/achievement. Bungie would know not to decouple the multiplayer from the singleplayer, as that would just weaken both. Destiny isn't an example of an "in addition" situation. Destiny is Destiny as a whole. There's no "without the bullshit" in its model. That's not to suggest that such a separate mode wouldn't have benefitted Halo... but there's also not much reason to believe that someone playing Destiny now would be playing Halo for providing a neutered version of what Destiny provides today. Warzone can just as easily be pointed to as an additional mode that doesn't fuck with Halo standard, but it wouldn't be simply because Halo is no longer as big as it was when Firefight was introduced.
[3] There's nothing concrete that proves either way... both of us are speculating in this regards... but as someone who has been a fan of a lot of series that lost their places in the market to changing trends, I think it's incredibly optimistic to simply say "you could have just made it good". To me, that's like telling a Blues artist that if they'd innovated like Justin Bieber did, then they'd have a larger audience still. They probably could've done exactly what Justin Bieber did... but simply being a Blues artist today makes that level of popularity super unlikely regardless of quality.
[4] I gave a more detailed reply to this already, but no, I'm not saying that. Though I am suggesting Overwatch's ability to cater a majority FPS player's preferences is a large contributing factor to its success. Are you seriously suggesting "good game = success" (and vice-versa)?
[1] what you are arguing it was easier for Halo's competition to innovate because Halo was more popular. You are underselling the accomplishments of Halo's comp. in the eyes of the market, they met the standard set by Halo, then passed it. There's no reason Halo can't pass the standard it set. You're basically saying it's easier for the underdog. Which makes no sense.
[2] again, destiny's integration of its various systems isn't neccisarily how Halo would have had to implement such system. Halo has always had disparate systems complementing each other. Forge and Firefight, for example are completely different addative components to Halo's core system. There's no reason to think a
additive co-op experience wouldn't have been seen as an innovation for Halo. Hell, forget Destiny for a moment- if Warzone was Reach's additive mode, and the core mechanics didn't change from H3 for arena and campaign, i believe the game would have had much more staying power.
[3] no I'm extrapolating, you are speculating. Halo 3 was the most popular FPS on the planet, despite assaults from a ton of other FPS. All signs pointed to people wanting H3 to be the bases of a sequel. Yet Reach went in a completely different direction. Your analogy does not compute:
What we have is the equivalent of a Blues Artist being the biggest artist on the planet and his last album was the biggest album ever released. For his next album, he makes a blues-pop album, purely because Justin Beber is the worlds second biggest artist. His longtime fans don't like This new album nearly as much and he doesn't gain many new fans. He makes blues-pop for the next 7 years.
Instead of drawing the rational conclusion, you conclude that people just don't like Blues as much as they used to- which is baseless, because no one has released a true blues album for 10years- and the last time one was released, it lit the world on fire. All we know is people prefer Pop over blues-pop.
[4] "good game" is a better catalist for success than throwing out core principles that helped propel your game to the top of the world in favor of principles that work better for other games.
Interestingly halo used to be very approachable. I'd argue CE-Reach are more approachable than OW, because there are no characters to learn. The addition of new mechanics has made halo much less inviting to new players because there are so many more inputs to consider, and the way mechanics interact with each other is more complex. (If you wanna run, you can't shoot or heal, if you wanna jump and zoom, you'll float- unless you turn that auto-feature off and tie it to sprint button, some jumps require you to zoom at the peak of your jump, if you want to melee while airborne your have to allow for a .3sec delay because the game has to be sure you don't want to ground pound. Some jumps require you to sprint-thrust-jump-groundpound cancel-thrust-clamber, etc.... you used to just run, jump, shoot, and throw grenades)