Vid Quality Is Not Great

[Flipsonic]

This is not the final product. I just wanted to test how my settings look on YouTube. I feel that the quality is not great. I have seen some awesome looking vids on this forum which blows this one away. This one looks pixelated especially during shots above the blue water (40 secs & 1:40 secs). It's also a little grainy. When watching from my iMAC/iMovie 09 timeline, the quality is not great either. I'm sure what's wrong is a combination of things. I hope its just settings on my camera or my not so powerful desktop and software. I hope there is nothing wrong with my camera. Any ideas what could be wrong?

Here is the YouTube version. Make sure you have quality set to 1080p.

Here are the specs:
P3P
ND16 filter
Litchi 1.10.0 IOS
Exposure - didn't realize it was set to Auto. It should have been on Manual. But don't think this would contribute to bad pic quality (?) I will reshoot this in Manual.
Vid Size - 4096x2160 24/fps
White Balance - 5k
Dig Filter - D Log
Image Size - 16:9
Sharpness - Soft
Contrast - Soft
Saturation - -3
Hue - 0
Metering Mode - Center
AE Lock - Disabled
Vid Format - MOV
Anti-Flicker - 60 Hz
Video Standard - NTSC
Post Pro - exported from 4K to 1080p. iMAC early 2009, iMovie 09. Yes its old but that all I got for now. Not much to play with when it comes to video effects.

 

[Flipsonic]

I'm almost certain this is due to iMovie 09 not being able to handle the amount of data and exports it compressed. I'm just noticing it now since this is my first shoot over a big body of water. If anyone is using iMovie 09 can you confirm? Or any other issues I should look in to, let me know. I know, I need to get a better post pro app.