The 12 hours here refers to the delivery window on the delivery day, not the time to ship the package. Though the total delivery time is certainly much less than 4-6 weeks.
I don't understand your comment. Do you mean that we should back to the 4-6 weeks delivery or if you're just annotating the notion that things have improved in the the last few decades?
It's that a 12 hour window being "crappy" is like saying your transatlantic flight being delayed 30 minutes is "crappy" (my first Atlantic crossing took 10 days I think). It's all about perspective :-)
Once we have a taste of what's possible it's really hard to accept that the status quo is good enough. With Prime Now I can get a lot of things ordered, shipped, and delivered within 2 hours, with live updates when the delivery person is on their way and arrives outside my house. I remember the days of multi-week ground shipping, I'm really glad we kept pushing the limits.
How perspective changes. I remember when ordering anything meant "4-6 weeks for delivery".