Your argument implies sprint is the sole reason Halo 5's numbers dropped after release, which isn't the case. Halo 5's initial focus lacked basic staples of the Halo franchise, ranging from modes like Oddball and King of the Hill to series staples like Big Team Battle and social playlists. Warzone is the most popular aspect of the game, but I hardly consider it more than a distraction from Arena.
Furthermore, Halo 5 has never really addressed consistent issues in the Arena playlist, like smurf accounts and chronic quitters (and don't say putting a penalty timer on quitters is going to stop ragequitting; people who quit are going to quit regardless, and the timer just ensures they don't come back).
Competently implemented quitting penalties will go a long way to prevent ragequitting. At the very least, it should be possible to ensure that quitting is extremely infrequent in matches between high level players. If a persistent quitter gets banned for twenty four hours, or a week, you can be damned sure you'll see less quitting.
I enjoy Halo 5 quite a bit, but when it comes to the game proper, it was feature-barren at launch and took ages to come into its own. If it launched as it is right now, it'd be lauded for its feature-rich gameplay and potential for growth. As it is right now, it's a great game that is in need of some attention to fix some issues I feel have been in the game since launch.
Perhaps. It's telling that Rainbow Six, which launched just after Halo 5, so very poorly, is now far above Halo 5 in the charts.
Halo 5 was in development long before any of those games released. The beta was playable back in 2014, and we knew what was coming as early as Summer of that year--just three months or so months after Titanfall's release, and just barely after Advanced Warfare's multiplayer was revealed, and certainly long before anyone had their hands on Destiny. People say Halo 5 copied those games, but the reality is those games were all developed currently, and their similarities were more due to trends in the games industry pushing towards unique methods of movement in shooters, rather than the glut of boots-on-the-ground shooters that plagued the market for over a decade before.
You say that there were "trends in the games industry pushing towards unique methods of movement"... but they are almost all identical. Maybe it is purely coincidental, but one way or another, I'm pretty sure every one of Halo 5's movement abilities had already been done by the time Halo 5 released. Hardly ideal when you want people to be excited about your new game.
Furthermore, smart-scoping is cosmetically meant to be an "ADS" function; it behaves exactly like zooming in in previous Halo games does, but with a physical animation to it instead of a black overlay with a circle and reticle in the middle of the screen. Being shot also forces you to descope, just like previous Halo games. Case-in-point, zooming in with the CE magnum or H2 battle rifle functions exactly as it did in those games, with the exact same functionality as the Halo 5 magnum or battle rifle. The only difference is what it looks like when zoomed in.
It doesn't behave exactly like zooming in does in previous Halo games, and you must know that. Some weapons behave the same scoped and not scoped. Some behave differently.
Additionally, 4v4 arena battles weren't a thing Call of Duty invented or even popularized; Halo 5 brought back a more standardized competitive shooter arena because it was reflective of the 2v2 and 4v4 matchups of CE and Halo 2's multiplayer modes, respectively. Also tangentially related, Call of Duty is 6v6, not 4v4. Big Team Battle has been a core part of Halo for years, yes, but it was not the sole aspect of Halo. The entire series' competitive scene has always been 4v4 infantry battles; not a Warthog in sight.
I think you've kind of nailed it. The competitive scene has always been 4v4 infantry battles. Halo 5's Arena mode is built around the desires of a tiny minority. Halo's CORE experience has -always- featured vehicles, and not just in Big Team Battle, but in almost all of its ranked playlists too. Team Slayer, its most popular ranked mode, had vehicles on numerous maps, and as such, you could play Team Slayer, a single game mode, for hours, but feel like you were getting a lot more variety than you can in any of Arena's playlists in Halo 5.
I feel like with Halo 5, 343i decided they wanted to build something for everyone. They built Arena for the competitive scene. They built Breakout as an attempt to woo the esports scene. They built Warzone for the casuals (and to generate revenue). They even put in Big Team Battle to appease those who were going to be revolted by Warzone.
Unfortunately, Breakout is too limited and doesn't feel like Halo. Unfortunately, Big Team Battle was a lazy attempt, cobbled together without thought or love.
What's left are extremes. Arena, too serious to a fault, and Warzone, which replicates the worst of pay-to-win. I played Warzone for an hour before deciding to never play it again. I played Arena for a month before losing my enthusiasm because I felt like I'd seen it all already. I'm clearly not the only one, given that the game is behind so many other shooters.