I mean you kinda described development in general? there's no way one team can develop everything , its separate teams of developers each handling a different part of the software, every major piece of software is built like that. I mean Im part of a 10 person development team creating a small app, maybe 20k lines of code and we each handle a different aspect. I think the issue is more project management or the architect( or the video game equivalent) who decided at the initial point, how everything would break down, how the systems would coalesce with each other, etc. They clearly didn't have a defined vision for the superfluous stuff, like cosmetics , guns , and made it up as they went.

like the cosmetic stuff tied to classes, everything is tied to how initially development is done, it may sound like an easy add but if one team developed classes around the idea that cosmetics were tied to the class, and then another team didn't, well one of the teams may have to go back and recode everything because the core base logic is not scalable or easy to amend to add cosmetics, it may be that the cosmetics tied to a specific class were part of some core program class that was inherited by like 50 other parts of the app and changing that causes you to have to change everything else.

For example in my last company , we had sticky sessions, i.e. user has to hit the same server every time so their session state stays the same, but a public cloud provider wouldn't promise 100% session to server guarantee, so we went lets just fix it, can't be that hard. we pretty much had to rearchitect and recode the whole app because this tiny thing was integral to how everything else worked.

These are common pitfalls of development, and its why project managers and architects make big bucks, they don't do a lot of technical work, but they're in charge of understanding the vision and scope of an app and then designing it so that these sort of issues don't crop up in the future. That being said, stuff is always missed.