A "diagnosis" is basically a cluster of symptoms and signs, that were described by astute clinicians who tried to put order into the chaos of medicine.
A diagnosis, is no more than a tool and not a goal within itself.

In some diseases (such as the ones I treat) you can actually see the cells inflicted by the disease. This makes it much easier (even though we too face problems every now and then, in making the exact diagnosis and also in deciding regarding the extent of the disease).

In other diseases you can't see the cells so you have to use surrogate markers, which are various tests that have been found to be positive in the vast majority of those who have the disease, and negative in the vast majority of those who do not have the disease. But, mostly rely (just like those who initially described those diseases in the past) on your clinical skills.

As to treatment, one always has to balance the potential risks against the potential benefits. There are circumstance in which it is a "no brainer" to decide on potentially harmful treatment, because the risk of no treatment is enormous. But, more times than not, the risk/benefit ratio is not so obvious.
Under such circumstances every factor has to be taken into account, including the patient's preference. (some patients are ready to take any risk for a possible benefit and others are the exact opposite).
Sometimes a "wait and see" approach is the best, not because the patient is not ill and couldn't benefit from treatment, but because the currently available treatments carry much more risk than the illness itself. Or because with the currently available treatments there has been no advantage (or even harm) with early treatment.

Lupus (very much like MG and many other autoimmune disease) can be a very mild illness requiring very little or no treatment or a life-threatening condition requiring aggressive treatment. It requires a good physician with a lot of experience to make those decisions, together with you.

Neither the fact that you "look good" and are able to lead a good life, nor the fact that your illness doesn't fit the exact "box" (Procrustean bed) of the diagnosis should be the factors that decide on your treatment.

I have had patients with leukemia who looked good (which to me was a reflection of their healthy self, we had to fight for and only more of a reason to fight their illness) and patients with leukemia who didn't exactly fit the "box", and had I take this approach none of them would be alive and well today.

In the early days of my training being very puzzled by the fact that the morphology and the cellular markers of my patient's malignant cells didn't fit (so I found it hard to make an "official" diagnosis and start treatment for that specific type of leukemia), I consulted the head of my dept. who said- I don't understand why you expect a malignant cell to know what kind of proteins it should express on its cell membrane. Trust what you see before your eyes.

Medicine is not an exact science and expecting everything to fit, leads to exclusion of too many patients. It can also lead to serious management errors. Sometimes what doesn't fit is a clue to a different underlying mechanism and leads to a different treatment approach. Sometimes what doesn't fit, should just be ignored because it is of no importance (and this again requires clinical skills).
And sometimes even the best physician doesn't know and errs on one side or the other.