I watched the G.-vs-Rusty-6-0.dmo , I didn't see any of "going to the lines with 100% power shots all the time".
What I saw is someone who barely can sustain rallies. You did 0 fault, though, so at least you got the basic of the controls correctly.
But it seems at this point you have very very low reflexes, and thus you have no chance to compete against a seasoned player.
I'm not sure why your reflexes are so low. Do you feel you see the ball clearly ? Maybe you could make it a bigger (in In-Game Menu -> Options).
You even run in the wrong direction on return of serves. Is it because you try to anticipate & guess wrong ?
The difference between TE and most other tennis games is that you have to work hard to learn how to run & position yourself. And as long as you didn't learn that, you can't hit consistently in the rallies.
So at this point you can't progress playing like that, it's just too hard for you. It's same than in real tennis, if your opponent is too strong, you get bashed and don't learn anything. So I'm going to quote myself :
You should really take it easy at 1st and take your time to learn the game. Play a while with the Danger & Aiming preview against the CPU, then only the Danger Zone still against the CPU, then play online with the original game (ie: not ITST Mod) so you'll still have the Danger Zone, and you'll also have more chance to find low skilled players (tennis isn't much fun when playing against someone a lot stronger than your). After 50 or 100 hours of this, you should be able to get back to ITST.
As long as you can't reach short ball when you stand far, you'll have to work on your reflexes and/or see the ball trajectory.
Your current goal should be to beat 6/0 the CPU at Club-10 level on the Blue-Green cement, with the CPU having 50% in all his skills and you having 75% in all your skills. When you do that, you raise 2 sublevels and give 5% more skills, so you try to beat the Junior-2 6/1 at 55%, then Junior-4 6/2 at 60%, then Junior-6 6/3 at 65%, then Junior-8 6/4 at 70%, then you should be able to compete against Junior-10 at 75% (even if you lose) and at this point you'll be ready for online mode without ITST..!
(and after more training, you could go back to ITST)