I believe the point is that if the chance of suicide is very small, and the mentally ill are forbidden from owning guns, it would seemingly be at odds with the claim that "over half of all quoted gun deaths" are suicides.

I don't see the direct connection between the suicide risk of a single gun owner and the ratio of suicide to homicide in total gun deaths.

The claim regarding suicide vs homicide is easy to confirm (https://en.wikipedia.org/wiki/Gun_violence_in_the_United_Sta...). It is not possible to predict every suicide, the best we can do is make an approximation using obvious risk factors like hospitalization for mental illness. There are millions of gun owners in the US, so yes the chance of a suicide is small.

How is it at odds with that? That is a fact, not an opinion. It's true that over half of all quoted gun deaths are suicides, and it's true that the chance of suicide is very small. The great majority of gun owners don't commit suicide. There's no contradiction.