Thank you so much for bringing this topic up! I am dealing with the same problems you are, but mine are a little worse. I have 2 properties on an abandoned golf subdivision and they are brutal. I have long been playing with these lawns and have 2 customers that are constantly threatening to leave our services. I met with the irrigation guy last week as well as the customer. I cannot get the soil probe into the soil more than an inch if at all. There is heavy thatch which I contribute heavily to lack of root penetration.
These 2 houses are over 6000 square feet and are beautiful and the truf is 1/2-3/4 acre, but what my research shows is that when the builders come in, they rob the property of all "soil" down 6 inches until they hit the hard pan and sell it before breaking ground for the house foundation. They continually destroy the hard pan with equipment and then apply what they call "top soil" when it is time to sod. It looks great for a year or two then the lawn stresses and eventually dies.
My research has proven me correct in thought because after meeting the irrigation guy and coming together instead of pointing fingers. He told me that during his install he rented a bulb auger with a larger bit to install the irrigation heads and each hole was an extremely labor intensive battle.
His suggestion is to water this property daily as an experiment(this year has been rough because of the intense heat and lack of natural rain). So we are watering every day for 40 minutes a zone and the property has head to head coverage. I have been monitoring it almost daily. I arrived yesterday with a soil moisture meter and found this. I touch the tip of the probe to the thatch as the zone shuts down and the meter goes to a 6, penetrate the thatch and touch the hard pan and it dives to 3, penetrate the hard pan and the meter reads 1 and sometimes none. I have zero water penetration into the "soil".
I have had relentless conversations with tons of companies. The best method I see which is less than desirable is gypsum constantly until some loosening is seen. I would use a wetting agent so the water is penetrating the thatch and carrying the gypsum past the thatch and SLOWLY working the hard pan. As a corrective rate, SOL-U-CAL-S goes down at 12.5 pounds per thousand so be prepared. Once the soil starts to loosen I would try to aerate, but if the machine is equal to running it over a concrete pad I would stop. Until it penetrates the hard pan, gypsum more and more and more. Once you break it comfortably then top dress with a high peat moss content compost and tah dah you are just beginning.
So where does this get the property? Nowhere slowly!!! I have been smashing my head against the hard pan and not to save the customer but to come up with a solution short of a full tear out and redo4! I have numerous properties like this. The only method is simple but unfair, bulldozer and start over! People buy houses and get screwed on things not covered under warranty and the lawn is one. It looks awesome when it is spoon fed and the thatch/roots are soaked in nutrients but it kills it in the long run.
Sorry for the rant and lastly! I will not ever try to run my splice seeder over it again nor a dethatcher. It tears it up but the new seed, rhizome creep takes forever to happen if at all because the thatch has to stay moist to convince the roots to live upstairs unhappily in the thatch!