One of my family also had myopia and Class 3. The myopia seemed to progress even after 40 years of age. Yet it ended in the medium range (not severe > 4 D). It might be like the progression is due to ciliary spasm only, as there also was presbyopia.
I have Class 3 malocclusion and severe myopia. One of my eyes also has high astigmatism (I define it as > 2 diopters CYL in contact lens correction). On that side I have worse malocclusion with lower molars tilted inwards. Wearing the dental splint for a week to neutralize those seemed to lower corneal astigmatism by 0.37 D and confirmed by keratometry, but the results can be due to other methods like longer time not wearing correction for astigmatism or modified eye exercise set.
@Ursa can we clarify what high astigmatism does mean?
Class 3 is the most rare malocclusion - only 1-5% of White population have this class. Perhaps it’s comparable to people having more myopia than usual (1-3 D) or progression (even 0.25 per 2-3 years) that did not stop after 20s.