If tanter is a countable noun, can you give some examples for uncountable nouns which are used with mye/mer/mest? In these lessons we used mange/flere/flest the most (mest). Or have I now give an example myself?
If you replace 'du' with 'dere' then it makes sense. In English you can add an 'all' to 'you' if you want to make it clearer.
And it can be a simple exaggeration. Like two kids bragging : 'your father is strong but mine is the strongest'.