I think you and I are both new to this world of DIY audio (pardon me if I'm mistaken about that), so given we likely have similar understandings let me take a stab at explaining what I think KK and Khron are saying.
The original post did not just add a transformer, they modified the circuit completely, adding a FET stage that is driving the transformer in a more meaningful way, such that it does actually have impact where the NT2A circuit would not do that alone.
I'm probably also not fully understanding, but I think the point they are making is twofold. One being that this modification is far more than adding a transformer and two that the idea that a transformer in and of itself adds something audibly valuable is not necessarily true, what it might add is a function of how it works in the specific circuit (such as the examples you mention of well known transformer coupled circuits).