Art style and design are two different things too, but both are part of the graphics. The art style has been different in every single Halo game till this point, designs have stayd consistent for a few games. Graphics instead are the most criticized thing in the trailer. My critics skip over the graphic fidelity, I would spend days on how bad the graphics are in the new trailer. I totally agree: 343 nailed the old design, but I'm arguing that's not a good thing, it's a bad thing instead. Good design tells a story, bad design doesn't tell any story, awful design tells the wrong story. I don't know if I can be any more clear than this, but the old design, while people may love it or not, has little to do with the Banished. The old design says that the Covenant has never been defeted, and the Banished are the same thing as the Covenant.
Graphics and Artstyle are two different things though. The more smooth, simplistic designs of both Master Chief and the Covenant (now Banished) have always been this way and in my honest opinion should have never changed. I agree the models for the Banished Brutes could use more sharp edges and the models could use some more grit and scratches, but I don't feel their armor designs are bad. The Elites, Grunts and Jackels finally look like Elites, Grunts and Jackels again, not Brutes in Elite armor, Goblins,and Raptors with shields like they did in 4 and 5. I mean you can have your opinions on the designs, but I feel 343 nailed the more classic designs of these characters.
Chief was designed with the old artstyle in mind, and its one of the few aspects 343 actually got right imoThere are things that work with the old art style and things that don't work anymore. I'm not really sure if Chief design is right or fitting, but I don't see any major design flaws yet, and I agree, he actually looks good. Speaking about the rest though, no mater how much 343 is willing to lie to it self and the community, the overwelming majority of comments about the last trailer, both those who liked it or not, all criticize the graphics in some capacity.
The problem with that is though, the designs they had throughout 4 and 5 ruined the lore of the Covenant. The Elites were to big, and brutish to be the warriors they were designed to be. Hell Halo 5's cutscenes showed the issues of the Elites and how slow and bumbling they were. The Grunts can't breathe oxygen, so it makes no sense for them to be designed where their mouth is exposed, the Jackels were excellent marksmen and had extremely good eyesight, and their old design did a great job conveying that while the new design, did not, they looked like they should not be able to hit the broad side of a barn let alone be the terrors they were on Legendary Halo 2. They had designs that complemented their lore and 343 basically designed them, almost the opposite of what they would do. Now they actually feel like themselves again, rather than a bastardized version of them. Also, Halo 2-3's Master Chief is just more iconic, then Halo 4's and 5. The armor just did not work for Cheif and felt more like a hindrance to him that an upgrade. Spartan 2's are supposed to be agile and sleek and Halo 4 and 5's armor did not give off that impression, it made him feel to slow and tankish despite it being the same armor he was wearing. Also the lore in how he got that armor was muddied and just not believable. Also, 343 has stated the Banished are essentially a ''Rebooted' Covenant, so in a sense yes they are not defeated in that since. Also even with the empire gone, you are not going to dissolve an empire that has existed for thousands of years, in less than 10 years, there are still Remnants out there, the Storm Covenant is evidence of that. Also we know nothing about this "Harbinger" 343 mentioned, if I had to make a guess, that is another "Covenant Remnant" that worships Cortana, (I mean that call Cortana made at the end of Halo 5, had to mean something" so the more traditional looking Brutes, Grunts and Jackels might be a part of the "Harbinger' rather than the "Banished" and the Red and Black Brutes are the actual Banished, and we wil see more of them later on. I mean, the fact that Jackels exist, means they have to be a part of another faction considering the Banished did not have Jackels in their ranks.