For five hundred years every size was its own drawing: sturdier, wider, looser as it got small. Phototypesetting replaced them all with one scaled master, and something real was lost. Left: a display master scaled down, the photo-era way. Right: true optical sizing, the opsz axis redrawing for each size.
Look at the smallest lines. The scaled display master turns spindly and tight, its hairlines starving, exactly what happened to text faces after 1960. The optical version thickens its thins, opens its counters and loosens its fit as it shrinks, which is what metal punchcutters did by hand at every size. The variable-font opsz axis is not a novelty; it is a restoration, and on a bloom-limited waveguide it becomes load-bearing again.