For most houses in the south, if your having humidity problems in the 75F range your system is to large. AKA, flipping the AC on, and blasting a lot of air with

For most houses in the south, if your having humidity problems in the 75F range your system is to large. AKA, flipping the AC on, and blasting a lot of air with a 35F drop into the house, then cycling off for 70% of the time doesn't remove nearly as much humidity as just running a smaller system closer to 100% of the time. Further most homes not built in the past 15 years are hugely flow constrained and mis balanced. So the AC runs, but doesn't provide even airflow so there are hot/cold spots. For areas where its not 90+ out for 8+ months a year, a large part of the comfort of the newer systems (and their larger SEER ratings) is that they can run at 1/2 speed (or whatever) to keep the AC unit running longer. Plus they are frequently sold with duct work upgrades. This is also why a "properly sized" system with a high EER can frequently save money over a high SEER system with a lower EER in FL/TX/LA/MS/etc. The problem though is that pretty much 100% of AC companies are just going to put in the same size system as they took out, and the home builders are just seat of the pants overspecing everything. It should be possible to determine heat load, and TXV flow/etc over a year, and then come back and resize the condenser/evaporator/airflow to go just slightly over the worse case. But no one is going to do that, and if they mess up and the customer can't keep the house at 78F when its 110 out, its going to be a costly problem to fix. So, better to just overbuild everything and deal with the significant efficiency decrease.