The article mentions this and also shows that cost per gram has gone down as well.

Smaller pieces are probably also more dense; less internal air.

I agree. I think there may be a dimension that's missing that isn't accurately captures in weight/pieces. I remember the Lego castles of old being large - the ones I see today in shops for $70 are like one piece of a wall.

OTOH, it might be that I was physically smaller when I made those memories, so they just seem smaller today.