Watching again all the videos I see that it is stabilizing and that is good. You know how to successfully control throttle and that is good. How much throttle stick does it take to lift off? Less than one fourth?
The other quads that you have flown, did they have a spring on the throttle stick? Did they have sensors to help you control the altitude? Flying without altitude sensors needs very small corrections on the throttle stick. Forgive me for saying, because I don't know your experience. You can't just set the throttle stick to the middle and expect it to hover. You must find the place where the power is correct for hover. Sorry if you know this already, but I can't tell how much throttle stick you are giving.
1mm is the difference between climbing slowly and descending slowly. Moving the stick down 10mm from hover power makes it fall quickly. In a hover, you will be always moving the throttle tiny amounts. There is no stick position where it will stay at that altitude.
I actually have 3 of the eBay clone of those quadcopters.
It is very important to balance your props. If you have not balanced them, please do.
With battery and USB plugged in, go to Input page in GCS. Switch transmitter on. Do not arm. Move the throttle stick. You should be able to see the GCS Throttle slider move with the transmitter throttle stick. There will be a time lag (maybe one second) from when you move the transmitter stick to when you see the throttle slider move. Just make sure that a very low throttle stick makes a very low throttle slider. What would be bad is if the slider jumps way up with just a very small movement of the transmitter stick.
First of all, battery size: All of the following discussion assumes you are using a 3 cell LiPo. If you are running a 4 cell LiPo, the props should be about 2 inches smaller than I discuss.
motor and prop size:
My small motors are 2212 (internal size) which are 2830 external size. The important thing is that they are KV1000. My large motors are 3530 external size and KV1100. I run 10x4.7 props on all of them. It looks like your motors are 2212 or maybe larger, that is OK. The KV is the important part. What is your motor KV? It also looks like you are running larger props than I am. If your motors are about KV800, I guess you should be running about 11x6 or 12x5 props. If your motors are about KV1000 you should be running about 10x5 (10x4.5 or 10x4.7) props. If your motors are KV1200, you should probably run 9 inch props. If your motors are KV1500 you should run about 8 inch props.
It looks like you are running perhaps 11 inch props (from what I see), and the prop pitch even looks fairly high, like maybe 11x6 size. 11x6 props are too big if your KV is 900 or higher.
ESC calibration: I assume that you are still running the settings in Aung2.uav, so the CC3D settings that relate to motor speed are OK. What I am going to suggest is dangerous if not done very carefully!!! I suggest that you tie it down like you did before. Leave the props on. Plug battery in. Plug GCS/USB in. Transmitter not needed. Go to Output page and click Test Outputs. Very carefully move one slider SLOWLY to the right until a motor starts. At any time you can press the Home key to move the current slider to the off position. (The End key is very bad. It moves the slider all the way to full power. Do NOT use it with props on!!!) When the motor starts it should be very slow. You should be able to slowly move the slider up about half way before it has enough power to lift that corner of the quad. Stop that motor (you can use the Home key for that( and test the other 3 motors the same way. If any motor is too fast at low speed, then you need to re run ESC calibration. You can also test all 4 motors at once. With all sliders all the way off (left), click the Link check box for each motor. Now you can slowly move one slider and all sliders will move. It should not take off till about one fourth of the way up. There is no stabilization when you test it this way.
The previous test shows if the ESCs are calibrated well enough to allow low throttle.
I see that the PIDs are slightly modified because of previous tests. You should probably set them back to default values, but I don't think that is your problem.
Calibrations: Has Level calibration (Attitude page) been skipped? That isn't your problem, but it shouldn't be skipped.