Not everyone's story is that same.
I've been detecting near 40 years and the one thing I can say is newer technology has ALWAYS netted me better finds. allow me to present my case.
Our city park was established in 1883 to host one of only 2 authentic Mexican bull fights ever held in North America. In 1884, at the bull fight, there was an estimated 35,000 people who came. Wright Park also sits along side the Arkansas River which used to flood on average every 30-40 years until the 70's when Urban Renewal screwed it up and now it is dry. Each flood would deposit from 3-6" of mud in the park burying any coins very deep. The nice thing is it has created one of the best natural test gardens one could ask for. The large area has deposits that gradually slope from south to north as deep as 24". Because of this one can take a detector and start from the south and work north until you reach the depth limit of that detector. There are always coins there for a detector that can reach them.
Up until 1991 my hunting buddies and I had never found but the occasional wheat in this entire park. In 1991 I bought a new state of the art detector, a White's Eagle Spectrum, and everything changed. For the next 10 years I pulled thousands of coins from wheats, mercs,barbers and seated's we had no idea were there. After I had clean out all my Eagle Spectrum could find I again moved up to the DFX and again started pulling the keepers further down the mud fill. After about 8 years it started drying up again. I tried many of what people were reporting as deep machines, but not until I got the E-Trac did the keepers start flowing again. After some 5 years again it took the CTX 3030 to bring up the keepers. At this point I'm waiting for a new technology that will allow me to go deeper.
With a 124 years of deep trash it takes a very good target ID detector to make this park produce. I've had people bring their simple beep-n-dig machines and go home empty handed other than trash. I have a standing challenge to ANYONE who would like to prove me wrong about the high end target ID machines. You bring your detector and if you can come home with more keepers than me from the exact same area I'll pay for your trip gas, food and motel. If not, you pay your own way. That's how sure I am of what new high end technology can do.
Here is a picture of the outside wall that was built in the 30's. It is 24" tall. In 1930 when built the inside and outside were at the same height.
Here is the north area show the ground inside the walls pretty much level with the top of the wall. That means coins that were dropped in the 30's and earlier are at least as deep as the wall is high.