:And, "it's a new model" is absolutely a lazy explanation. I'm not saying it's not a good one. They changed the design of the Master Chief between Halo 1 and 2 because they wanted to make him look better, and came up with the "new model" explanation after the fact (probably).

That's still missing the point of what I said before. It's not a design upgrade. It's literally a different set of armor, performs differently, different shields, faster move speed, etc. Claiming it's just a design retcon of the same suit is like saying In Amber Clad is a design retcon of the Pillar of Autumn.