Why use a web browser? Or even a web server? Opening up rcp so users could download it and view it locally would be much simpler.
Of course, some people might want additional functionality, and to facilitate that functionality, we have many technological tools at our disposal which make the process of implementing that functionality simpler than not using them. What you deem to be simple enough without being too simple is based on your use case and preferences.
What are the requirements and what do you plan on building into it? Annotations? Persistent highlighting? Foldable sections? In-line bookmarks? Citation generators for quotes? Content editing? Comments? Image carousels? Dynamic reading lists? Searching for other papers using selected text?
Of course, some people might want additional functionality, and to facilitate that functionality, we have many technological tools at our disposal which make the process of implementing that functionality simpler than not using them. What you deem to be simple enough without being too simple is based on your use case and preferences.