Also humans would revert to explicitly using an algorithm and external storage like a sheet of paper with tally marks or a spreadsheet or even a computer progra

Also humans would revert to explicitly using an algorithm and external storage like a sheet of paper with tally marks or a spreadsheet or even a computer program if you scale the question up to a full sheet of text or a whole book or a collection of books (we probably do it at a single word size too, but it's more intuitive than explicit behavior for most folks when the count sum is around 8 or less). LLMs can't effectively execute algorithms similarly in their context, nor can they memorize new data or facts it was given without providing it tools like function calling or embeddings. If you give LLMs tool calling and storage mechanisms then counting letters in words becomes pretty damn reliable.