The very first letter in your example sentence started as an ox 𓃾 then via 𐤀 α etc. turned into a https://en.wikipedia.org/wiki/A#:~:text=1-,History,a – but even in the hieroglyphics it was used to represent the sound (the sound of the start of the word for ox), not literal oxes. The road towards more abstract / less pictorial systems was created for speed and ease of writing, not in order to represent more abstract thought. (Note also how alphabets are changed by the implements used to write them, e.g. runes for knife-on-wood, wedge incisions for clay tablets, square capitals on stone – this too was a pressure from ease of writing, nothing to do with representing more complex ideas.)