True, there are several moving parts within the app. I will try to tackle your response piece by piece hoping to justify my process:

• “Amazon caters to a broad audience” — Yes, I agree. Amazon has been around for almost 2 decades now and has continued to update and modernize their web and mobile experience based on the data they have collected. I want to gather more data on how people belonging to an older age bracket are using it. There are issues of accessibility to take care of such as understanding which typography to use, contrasting colors, UI component sizing, etc but the design itself is simplified to reduce navigational blocks.
  I tried to approach the study with the knowledge that where I was working from, I did not have access to connecting with people belonging to an older age bracket. Otherwise, I would’ve most definitely extended my study into the realms of accessibility for the elderly based on the data I collected. That is exactly what I mentioned as part of the further study, that I would want to collect more data to iterate over the existing concept.
• “Overlooking accessibility, workflow priority, design system” — The app comprises of a lot of moving parts and given the complexity it calls for a more extensive and deeper dive into the system itself. The study itself is not exhaustive and its always open to more additions. Then again, I would consider myself as ‘grasshopper’ in the domain of UX, learning to master the discipline. If you want to connect with me to share your knowledge about it, I am open to it! 😄