I worked on apps that doesn't needed anything other than concrete classes, I also worked on apps that really needed a project architecture in place. It never is black or white.

IMO it helps a lot to discuss the aim and intention of changes / decisions when working with others. PRs and RFCs are useful for having and keeping track of these kind of decisions. We're all responsible for what goes into the codebase thus we're all responsible on what happens in our product. I'd consider workplaces that doesn't provide healthy discussions as toxic.

Now speaking for mobile apps, while app performance is vital, IMO few nanoseconds can be sacrificed for scalability depending on the product requirements. That's mostly unnoticable in mobile applications if you do your threading right. Apps don't usually do heavy loads of work. Generally important bit is to deliver user experience with little effort ( in development time, testing time & publishing time ). It's an exchange like anything else.

It's good to keep in mind that everything is suggestive. Best engineers I came across had always consumed and digested multiple solutions to a problem, and they were concise about why do they use an approach when solving a problem. Solutions are right when applied to correct problem.