As someone who tried all kinds of EdTech, I'd venture to say that the key to education quality is not in tech but in pedagogy and student engagement. The pedagogy depends on the quality of teachers, or specifically the quality of lecturing and the quality of assignments. Good assignments are really hard to come by. They need to be tailored. They need to have progressive difficulties. They need to be designed to help students understand fundamentals. They need to inspire students. And very importantly, they need to be graded and reviewed by the teachers. All such will require dedication and ingenuity of teachers.
As for the student engagement, I believe it depends on the passion and curiosity of a student, but I also recognize that most students simply don't want to work hard, and therefore they need certain healthy pressure, or at least a specific goal. Maybe EdTech can make quality teachers and homework accessible to millions, but it's just hard to keep students engaged. On the other hand, there are enough amazing free education materials in libraries and on the internet. The barrier to access them is really one's motivation.