Not all data entries in every dataset is distinct, far from it. It seems to me, that you are trying to argue that big O is not useful, because you believe that

Not all data entries in every dataset is distinct, far from it. It seems to me, that you are trying to argue that big O is not useful, because you believe that an assumption of constant time comparison cannot be done. But I disagree, once we go into the realm where we cannot assume that comparisons are constant time, we are also in the realm where IO operations dominate the runtime, and we base our big O on IO operations rather comparisons. Here the bound and big O is even more relevant.