Halo is trying to be a jack of all trades master of nine. I wrote this before, but just compare the base experience of infinity Slayer vs team throwdown and pro Slayer.
You're getting two vastly different experiences, and in the end, the game is splintered.
Compare team Slayer in Halo 3, social Slayer in Halo 3 and MLG team Slayer in Halo 3. The base game is almost identical and that if anyone really wanted to, he can drop in and drop out of all playlists without really missing a beat.
Can someone play infinity Slayer for a while, then go and play team throwdown? Now the question becomes, is infinity representative of future Halo, or is team throwdown?
I have to disagree with this, Halo 3 had equipment and MLG did not. No bubble shield, no vehicles, no asymmetrical maps, no brute shot, radar vs. no radar (which alters the game drastically IMO)...you get the idea. Sure it was somewhat "closer" to the default game than 4's difference but it's a far sight from the default game. When you look at Halo 3 as you point out it had infection, doubles, MLG, objective, social/ranked and no one ever complained about the splintering back then. Why? The gunplay, damage, firing cadence and for the most part movement was all relatively consistent.
It hits home a crucial point, the masses don't want to have to train with a team, memorise spawn traps, force spawns or be on the receiving end of spawn killing etc. It's not fun and the big populations won't come back day after day for that. Sure it's damned competitive for hardcore or MLG players who practice callouts and spawns etc but it's not BTB, it's not default flag, it's not mid sized maps nor 1-sided maps etc. You may capture a certain percentage who want to drill/grind/team up to this but it has to be more than just the basics.
Even the largest population in Halo 3 wanted to play with vehicles and equipment and a variety of maps of differing sizes/shapes etc. Slayer and BTB have always out populated MLG or hardcore modes.
This idea that hardcore MLG from 3 alone can be the core gameplay for all modes is bullocks to be frank, with respect to the large populations. Tashi's ideal that gunplay should be a core standard across modes is ideal and that sort of standardisation is what allows the skill progression. If you cater to the top 1% or %5 you alienate the 95-99%. Ghost gets this and we saw good work in expanding the appeal of throwdown over say 3's MLG. I do agree with making the core game less random and more competitive but there's nothing wrong enabling a variety of modes with a solid core. Default has always been the more popular core, from 2 to 3 and Reach to 4. Halo 4 at launch forgot this, the MLG crowd do the polar opposite. I try to sit somewhere in the middle.
I feel Halo 4 now (not launch or Infinity) has very much for the most part succeeded in finally bringing that core and standardised gunplay/movement back. Reach couldn't do it, Ann. couldn't do it, 4 at launch couldn't do it and now we have a new studio, gunplay sandbox and real experience in unifying the "core mechanics" for all modes. The turbo update has really been a far better design methodology for Halo matchmaking, it's far from perfect but it's more rights than wrongs now.
From what I've gleamed from the survey so far to me the maps are far and away the most important aspects to what makes players love a game, even more than the mechanics themselves. The map design is decided in parallel to the gametype or working mechanics during development so it's inherent I suppose.
I think with some hard and fast decisions, which seems to be what you're suggesting more so, HX1 could really be something that clicks with the wide variety of players but drills down to the specific modes that keep individuals or teams come back day after day. Hardcore, default, casual fun or new players alike. The developers have this burden to deliver a competitive game that can shape shift but feel familiar and promote personal/team growth in many aspects. I agree nobody wants to win or lose based on a random personal ordnance drop, you'll see in my post above I never mentioned personal ordnance AKA Infinity.
Oh I feel like fun today? Action sack, but my guns basically behave the same. Oh my regular friends are on right now, let us warm up a match or two in social then hit up ranked slayer and get that next rank level up for everyone. Oh some friends are joining and dropping out during a night's session, we should hit up the 64 player mode with JiP and have some great Halo encounters...
I'm not trying to piss off a specific group but variety is simply a must, a core competitive game is also a must and the sooner we all get that and work to achieve what the developer is burdened with the more progress or good ideas we can come up with.