Like it was pointed out, MANY factors can affect the properties of a paint or primer.
In the data sheet for DPLF, it states you can recoat DPLF anytime up to a week, without sanding.
That tells me that DPLF needs at least a week to cure, and before a week is up, it is not fully cured. My belief is PPG formulated this property to aid crosslinking (bonding) with the next layer of paint or primer that goes over DPLF. This can also be useful in a shop where you can prime a car on a Friday afternoon, and not have to get the next layer of paint on the car until Monday.
A lot of areas in the USA, you cannot use lacquer thinner any more due to VOC regulations.
Are you still painting cars with lacquer?
Is DPLF better than SPI, or the other way around? If depends on you knowing the properties of both products, and READING THE DATA SHEETS ON BOTH PRODUCTS to know which is the best to use.