I would define "architecture" (as it appears in applied software development) as working on the structure and interaction of system components much larger than a single data structure or a single algorithm; where many of those components might be separate systems themselves. When "architecture" handles specific data representations, it's usually talking about the data representation and encoding at some API or "API-like" (e.g. file, message, etc) interface between two systems or persistent storage, not about the temporary representation of that data during some processing; and "architecture" is generally much more about the semantics of that data and possibly differing assumptions/expectations about that data between different components, rather than the performance characteristics of that representation for a particular algorithm except in the relatively rare case when a single algorithm represents the majority of that system's purpose and performance.