Ariel, I looked at ONLY the match you lost vs Dmitri, the last match vid you posted near the bottom of your post.
In game 1, you lost a LOT, I mean a boatload of points because you were playing upright like a center pole. You made a few BH loops or BH topspin receives of serves, but you made errors in every kind of shot. You would make a an opening shot, finish a little off balance to the rear, take a big step to the rear, then when opponent played a softer shot to you, your shot was an error, you were too far back for the ball he gave you. You did that a LOT. Depth control of where you play killed you.
In game 2, you seemed to make an effort to get lower, but as soon as you hit your first ball, you played upright again. Often, when you were able to see an easy chance to topspin, you would get down before you hit. You were more consistent and that won you the game.
Ditto for game three, you did a little better staying low and not missing shots. You were confident. You missed several BH loops by trying to do a BH loop when the ball was in your FH side.
You lost game 4 and you failed to realize was caused it and it cost you the match really. You made EIGHT errors on BH topspins of serves or long underspins you wanted to attack. WHY did you miss all of these??? If you look at teh vid again, you will see that on nearly every BH tospin you tried to make, you were too far back for the ball given and tried to loop the underspin ball when it was too far in front of you. Sometimes you were close to the table and just hit it way too far in front of you reaching too much. Sometimes you tried to BH loop a ball that was going to your FH. You cannot be 3 feet off the table or even two sometimes and expect to land a high percentage of BH openers vs those soft balls he was giving you. As the game went by, you kept trying and trying to fight through it, as you know you got a good BH opener, but you were so out of position (or too eager to get the shot off and NOT wait for the ball to come to your zone) Each time you went for such a BH, it killed you and overcame all the other good shots you made.
You made the same mistakes in Game 5 in critical points, and the same BH mistakes from game 4, although you fought well to come back into the game. If you were able to better control your playing depth, stay lower, and hit the ball in your zone better, you would have had that game.
Those things will come with more attention and work at it.