The other problem is that, whether intentionally or not, the two non-Chief focused games have shown that the Chief’s legend of greatness wouldn’t be remotely possible if it weren’t for the efforts of Noble Team and the ODST. As others have pointed out, the Collection’s omission of Reach and ODST has an underlying message of “those dudes that are more man than machine and died to help turn the tide of the war don’t matter, have fun with this hunk of metal!” In fact, once you go into those two games, the expanded universe, and the marketing, it becomes clearer and clearer that the legend of the Master Chief is much more compelling than the Chief himself.
Legends and folk tales can be way more interesting than the actual event that happened, and the Chief is a walking example of that. The way his enemies and allies talk about him make him out to be this legendary warrior able to shrug off anything that comes his way. But once you spend time with him, it becomes clearer and clearer that he really…isn’t. He’s got the Batman problem where his thing is that he always wins and has to to further prove how awesome he is. But where Batman fails because it’s in some ways part of his character and he makes sure not to make the same mistake, Chief wins because “well, he’s a space marine with super strength, so he’s gotta”. Dying in the games isn’t because the Chief has finally met his match, it’s because you went against the canon of him shrugging off more bullets than Superman on an average day.
Master Chief is more legendary than he frankly has any right to be, especially when there are characters who are actually characters and not just largely blank slates. For instance, take Halo 2’s co-protagonist the Arbiter, a Covenant shipmaster forced into his job to redeem his disgraced name. He’s a walking embodiment of “started from the bottom, now we here,” going from exiled Elite to their leader during the Covenant Civil War and the reason why the galaxy’s sentient population isn’t completely wiped out. Gravemind calls him “flesh and faith, but is the more deluded”, and this is what makes him more compelling, because he’s got an actual arc and is struggling to deal with everything he’s done for decades in the name of meeting a Great Journey is all a lie. Why isn’t there a game that shows what he’s been up to during the four year gap between Halo 3 and 4?
Keeping things firmly in the Spartan family, there’s still Osiris. What makes them different from the Chief, aside from the team’s diversified makeup, is that these people actually feel like people. They get their personalities across in that bombastic intro sequence not just by how they speak to one another, but by how they act in battle. Vale immediately goes for the Phantom because she has knowledge of Covenant tech, Buck charges ahead because of his ODST “feet first into hell” training, Tanaka latches onto her teammates and mimics what they do and is rarely alone during the whole thing (seriously, go back and watch it, she’s always next to someone aside from one brief moment), and Locke is confident enough in his team to let them do their thing.
In a trailer, Locke tells Buck that “he’s not the only one here because of him [Chief]”. It’s a way of saying that just because they’re the Chief’s siblings doesn’t mean that he’s above them, and it holds true both in the story context and in the real world. Halo as a franchise has grown much bigger than a silent man in a massive suit of armor fighting aliens, it’s grown to have dozens of characters and worlds that don’t revolve around the Chief. If anything, at this point, one could argue that the series has gotten to a point that it doesn’t need Master Chief, but Chief needs the series to continue being relevant.
