I do a lot of buying via Amazon. Paid for the "Prime" service a couple years ago.
I found that items didn't really show up much faster - maybe a day earlier - than the regular free shipping. Their two business days (or whatever the standard Prime shipping time is) didn't seem to include weekends, or holidays, or the day the item(s) were ordered, etc.
I don't know if I'd go so far as to call it a scam, but it's definitely a waste of money, imho.
Maybe it's better now, I dunno, but I'm content to wait for their standard free shipping, which is usually pretty decent.