I’ve personally watched it stop seizures first hand many times. I’ve always watched it stop a seizure before it even started. Until you see something like that first hand, you’re ignorant as to the medical effects and uses it has.
You cannot use the fact that there was no seizure, because someone got high. You cannot prove that a seizure is imminent. I am sure Doctors could with fancy equipment. MJ is a drug, it has benefits that stoners like, it does not have benefits medically.
And there have always been a myriad of other and better treatment options available.
Ten of 11 studies evaluating acute cannabis exposures reported a higher seizure incidence than would be expected based on the prevalence of epilepsy in the general and pediatric populations (range 0.7–1.2% and 0.3–0.5% respectively). The remaining two studies demonstrated increased seizure frequency and/or seizure-related hospitalization in recreational cannabis users and those with cannabis use disorder.