As far as I know there is no correlation between the severity of the symptoms at diagnosis and the chance for remission.
It is not unusual for a patient with crisis to fully respond to treatment and go into complete remission.

What does influence the chance for remission is how much time passed since the diagnosis till the beginning of treatment and also the type of MG that you have. MG is not one disease. There is AchR MG and MuSK MG and probably others not yet discovered. (several other antibodies have been found, but it is not clear yet if they can or can not cause MG-such as anti-ryanodine, anti-LRP4 etc. Those are also not tested routinely). AchR and MuSK are very different in many aspects.

MuSK MG is less likely to respond to treatment, AhcR is more likely to respond.

A significant proportion of AchR MG patients do well with a low dose of immunosupressive treatment or can even stop all treatment.

Most MuSK MG patients require higher doses of immunsupressive medications for prolonged periods, have more steroid induced myopathy and a less stable disease with many recurrent exacerbations.

Some patients with relatively mild forms of AchR MG can probably do well with mestinon alone.
Most patients with MuSK do not have a good response to mestinon, and require other medications.

Finally, some patients do not have autoimmune MG but a congenital abnormality of one of the proteins of the NMJ.