I agree a 12 week randomized controlled study would be sufficient to determine if A2-73 improved seizures, if anywhere near the number of patients were studied as in recent phase 3's you mentioned.
However, this study is only placebo controlled x 7 weeks with n = 15 probably split into 3 groups (5 placebo; 5 low dose; 5 high dose). Those phase 3's mentioned in your post were 10-20 times larger with > 200 patients.
Furthermore, the 2 ongoing small studies are in adult Rett girls with the classic MECP2 deletion and having active seizures is not an inclusion criteria. Although 90% of Rett girls have seizures at some point, only 57% of classic Rett girls followed for an average of 5-6 years had seizures while enrolled in a large longitudinal study (Kaufmann is one of the authors). Seizures become more and more uncommon with age into adulthood, so even fewer would be expected in Rett girls in their 20's to 45.
Therefore of the 15 girls in the US study, maybe 8 are at risk of a seizure over 5 years, with some having frequent seizures and some rare...so maybe only 3-5 would have been expected to have one or more seizure over a 7 week controlled period.
From the paper: "Among the 778 participants followed longitudinally, 54.3% (423) had a history of seizures before the study, 56.9% (443) had seizures at some point during the observation period, and 17.1% (133) experienced their first seizure during the study." ... and this was over an average of 5.5 years