"Cheating" is subjective, but you are correct. To put it in more neutral terms: Using the known 2309-word list of solutions, hard mode can be solved 100% of the time within 6 guesses. Not using it, you would need 7 guesses to guarantee that you solve it every time [1].
The subset of words that are solutions is an internal data structure of the game. It is clearly cheating to refer to that list. If you are willing to examine the inside of the game's black box, the optimal strategy is to simply extract today's answer.
As a human, you already have knowledge which is similar to knowing the internal dictionary: you can judge what other kinds of words Wordle is likely to avoid (uncommon words, proper nouns, plurals). So I don't think it is cheating.
Thing is, you can develop a very strong intuition for which words are in that list: they're all common words and mostly "main dictionary entries" (you probably won't find a 4 letter noun or verb with "s" tacked onto the end, probably not "ed" or "es" either)
Certainly using the exact list is a step beyond that; but you can in fact get very accurate at guessing which words might be on it without memorizing the list
In the limit, if there was one day of Wordle left and you looked at what it was going to be and then told me that the optimal strategy of which words to guess is to just guess the solution as the first guess, that's cheating. Your "strategy" becomes a question of how well can you compress the list of solutions into the entropy allowed by how you chose to express your strategy, in this case "four 5-letter words" or somewhere between 20 and 94 bits of entropy[0].
[0] 4*5 assuming that 1 letter is one bit of entropy, which is a rule of thumb when you're compressing gigabytes of text to log2(26^(4*5)) if we just count the combinations of letters
