Sad little bloom…why?
 

This is the third blooming of my Charlesworthii x, and this bloom is decidedly smaller, thinner, and generally quite pathetic looking compared to its large and in charge predecessors. Seems strange since the plant is so much bigger now. What did I do wrong? Too little water? Too little light? Too small a pot? I suppose this could just be a one-off, but it seems more likely that it's caused by culture inadequacies on my part.

Have you done anything differently in the culture? I am not a Paph grower so that would be my only idea.

It's most likely none of those, but the plant itself.
Flower qualities on Paphs ( size, color, shape, especially the shape) can vary slightly to greatly ( bulldogs) from season to season.
Some plants consistently bloom nearly exactly the same way while others have more frequent hickups.
If you don't like the current bloom, you can cut it off and focus on growing and hope for a better flower next season.