For the non technical explanation IMO- the Gen 4 had a crunchy trigger. The words I used are crunchy and sponge like. Just during the trigger pull it didn't feel "good.
However- the Gen 5 is a completely smooth pull. One good motion with no issues. It's like a sturdy VP9- not as light, but very smooth.
Best comparison I can think of is my running shoes. The VP9 are lightweight running shoes that people like. However- I like a sturdier and heavier Asics running shoe bc I feel like it gives me better support. Hope that helps as I am sure there are people who can give plenty of detailed technical explanations.