Brunelleschi was a great genius, but his innovative design for the dome of the
Duomo was rooted in Gothic architecture, more than in classical ideas. His dome survived the earthquakes of 1510, 1675, and 1895.
A dome was long understood as being a rotated arch; in the case of the
Duomo, it was a rotated
Gothic arch (modified by the impact of a heavy weight at the apex, which was planned early on). This was very different from (and superior to) the hemispherical dome of, say, the Pantheon. The interior ribs of Brunelleschi's dome are influenced by the Gothic flying buttress. As with the earlier Gothic cathedrals, the key idea is that, if you plan carefully how the static loads will be transmitted, the amount of stone used can be reduced substantially. That's the same principle that gave us this structure, which is indeed the complete opposite of "dark":