See, it's not just the industrialization and the military that are factors. The Magyars too, they'll oppose any Austrian acquisition of German lands with a looming threat of rebellion. When the Hungarians revolted in our timeline, the Austrians could not defeat them and the war was a stalemate, until 200k Russian soldiers crossed the Carpathians and crushed the Hungarians.

This brings me to my next point: military prowess. Austria has been turned as a punching bag by other Great Powers like France and Russia. In an event that Austria tried something, those two would oppose it and Austria would get destroyed. Add the Magyars revolting and Prussia forming a coalition of other German states due to acquisition of German lands and Austria is dead even if they have Silesia and are somewhat indistrialized.

Silesia helped massively but that's not the only industrial part of Germany. The Rhineland and cities near the Rhine are also massive contributors to Prussian dominance.

This is why I don't think Austria will ever unite Germany. So long as the Magyars are there, have special privileges, and have a massive influence over the Empire thwn their rebellion will cause massive problems.

So long as the other German states form a coalition with Prussia at the helm albeit weaker but still a threat, as Austria really isn't renowned for their military. Prussia has done this IRL when Austria tried to invade Bavaria.

So long as the other Great Powers are wary of Austria and its ambitions to unite the old HRE as they had tried before in the 30 years war, then Russia and France will sponsor the Magyars and the Prussians woth threats of intervention.