This. I pour 5-6 glasses of wine from a bottle, and I don't feel that they're "small" in any way. Putting a third of a bottle at once in the glass is far too much - at that quantity, swirling the wine becomes nearly impossible. And anyway, holding a wine glass should be effortless, you should be able to talk & do mild gestures with the glass in your hand.
And these large glasses are used in many homes. I have no problem believing that people are drinking glasses of wine this big, mostly because I see them do it.
I’ve always found it easier to visualize drink quantities relative to a standard bottle, 750ml for most wine and spirits.
So that 250ml serving is 1/3 of a bottle per glass.