If you interpret the 1970s Lego parent letter as anything other than a sales tactic, you’re giving Lego too much credit. If I'm handing out a medal for the most gender-progressive company of the 20th century, I'm extending a hand to Slinky first. Beginning in the late 1960s, they jingled it clear for decades: this industrial spring is fun for a girl and a boy.
I will say, however, that my son and daughter enjoy Legos equally, and until today, I hadn't given it much thought. Maybe that in itself is the greatest sign of progress.