I feel like you're making progress! Your flights, while not necessarily prettier, are definitely getting longer, which means you are gaining control.
I watched your most recent playlist, and noticed a few things:
How windy was it when you were flying? There are times when your TT doesn't even seem to move relative to the ground. In these conditions, I'm not surprised that its difficult for you to get the hang of it.
I really feel like you should give rudder on the right stick a try. In your videos I can hear the motor changing pitch while you turn. It is notoriously difficult as a beginner to give rudder input without making accidental changes to the throttle if they are on the same stick. If you have rudder and throttle on two different sticks, it is impossible to do this, and it makes it easier to fly.
I also think I heard your gimbals (sticks on your transmitter) spring back to their neutral positions several times while you were flying. By that I mean it sounds like you were giving a control input, and then just "let go" of the stick with your fingers. This makes for very abrupt control inputs, and makes it very difficult to fly smoothly. I may be wrong, but that is what I thought I heard.
Try keeping your fingers on the sticks at all times. To make a right turn, push the stick gently to the right, and when the turn is as sharp as you wish it, push the stick slowly back to the middle or zero position. The plane will continue in the bank, assuming there is not too much wind acting on it. If your right turn becomes too steep, correct it with some left stick. Also be ready to add some up elevator (right stick back/down) as turning will cost some lift. When you want the turn to end, apply left stick until the plane assumes level flight. Then be ready to correct let or right if it starts to drift in either direction.
Are you able to dial in some expo in your transmitter? I am unsure what equipment you are using. Expo will help deaden the center of your control sticks and make your controls more smooth. Most FT designs like about 30% expo.
Finally, double check your CG or center of gravity. There are a few sequences where your plane is exhibiting a "porpoising" behavior when flying with the wind, meaning the tail drops and the nose is high. This is usually a sign of it flying tail heavy.
How to gain altitude with an underpowered motorglider (your TT): Keep the nose pointed into the wind. You will see that your glider will fly very slowly over the ground. Apply just enough up elevator to start a slow climb, but be careful not to push the nose so high that the aircraft stalls. In heavy wind, you need to maintain airspeed to fight the effects of windshear, especially when flying downwind. Finally, use the rudder to combat gusts and keep the wings as level as possible. Sharp turns will spill the wind from your wings, losing your lift and costing altitude. You want to keep the plane flat and pointed into the wind.
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