The problem lies with the H.264 codec, it's great for high compression and internet use, pure crap for editing on a real system. However, that being said, the same problem exists with video shot on GoPros and that footage is used everywhere and accepted by broadcasters. Today you can get away with average quality HD as long as the content is relevant, no one seems to care that it's so highly compressed. Then again, the P4 is a fraction of the cost of the old formula that would consist of renting a helicopter, pilot, and required mounts to shoot broadcast or film quality with. I recall plenty of $8,000 days spent in a Bell Jet Ranger, so the quality of this $1,400 drone is stellar at the price point and ease of use.
Ok to improve the picture quality here are my successful suggestions:
1) Put a ND8 filter on the lens and leave it there. Don't remove it unless you are filming after dark, it should ship with one because the images are not great without the filter.
2) Lower your sharpness setting to -3, your contrast to -2 You can bring all that back in post.
3) Find good transcoder software and convert to ProRes422 BEFORE you start editing anything on the timeline.
4) In post, add a flicker filter (set at medium), reduce your black levels, -15 seems to be about right on most days, then increase sharpness GENTLY.
Images look better tracking horizontally, vertical movement enhances the negative effects of high compression. The higher the altitude, the better things will look with this codec.
I have been producing HD since 1995, seen everything, and really hate how poor the images look with current compression technologies. HD looked spectacular 15 years ago, when things were lightly compressed and a camera cost $100K before the lens. The lens is more important than the imaging chip, and compression can destroy even the best quality equipment. However, there are few choices when reducing the size of the equipment and making it affordable enough for so many people to purchase and enjoy. DJI really makes nice equipment at this price point, so you need to understand the compromises you make with such purchases. Everything in this business is compromise, a balance of quality vs. cost.