The issue isn't symbol granularity. The way symbols work cognitively is they allow us to retrieve that which the symbol represents, that's what the symbol means. In the human case, its all the memories of states through time and the relationships etc to that symbolized object. So the symbol is effectively just a way to access the real meaning, so the symbol alone gets you no where.
Information (that can exist in a mind) is symbols + relations between them. It's symbols all the way down; even ideas like atoms are symbols. We ourselves can't tune into the very fabric of reality, so we abstract over it, and do a pretty good amount of useful reasoning over those simplified ideas
Your memory of an event and the sensory perception of it is not a symbol. However, a symbol can be used to help recall the memory of the event. I think maybe the issue here is the definition of symbol, and I go by this: "Something that stands for, represents, or denotes something else (not by exact resemblance, but by vague suggestion, or by some accidental or conventional relation); esp. a material object representing or taken to represent something immaterial or abstract, as a being, idea, quality, or condition; a representative or typical figure, sign, or token;"
Think about it this way: is a digital image a symbol?
It's as close as computers get to raw "sensory perception", but ultimately it's a collection of color values, each of which is an identifier that maps to something we think of as a "color", and arranged in an order that we've defined as representing X and Y positions relative to a light sensor
My point is there's ultimately no real distinction between a mental or digital representation of information, and a (huge) set of symbolic data. We have abstract symbols that refer to a cluster of more detailed symbols, on and on down to more and more granular levels. What you're thinking of as "symbols" are just the higher-level ones, but there's no fundamental distinction between those and the "raw" data, at least as it's represented in some kind of mind (digital or biological). It's all an approximate representation of real reality, which is impossible to represent in a non-symbolic way. What matters for "thinking" is that your symbols are granular enough that any conclusions you draw from them map usefully close to the symbolized reality.
>Think about it this way: is a digital image a symbol?
No, a particular digital image is not a symbol but output data from an image making event. It can be sybmolized however for easy reference to that particular output data.
