I have measured and washed hundreds of pieces of fabric.
I started measuring before dunking just to see what - if any - shrinkage occurred.
Fabric can shrink lengthwide, crosswise, or both ways. I found that it usually would shrink more one way than another. I have had Michael Miller black - from three different bolts - shrink over two inches in width.
I started to really become aware of shrinkage when I started measuring my cat prints - of which I had purcased a yard and now the pieces only measured 35 inches.
The shrinkage you experienced is extreme - but I have had a five inch block go town to a 4.5 inch block.
for me, it is worth the effort. I have also had fabric bleeds - and not much success in removing them.
now I soak everything In very hot water for at least a couple of bours -
Of those that say they don' t notice - how many have actually measured before and after?