First of all, the opponent has a weird ball (doesn't topspin) and he is reasonably consistent (which is what TT is really about). It is common to struggle against these players until you get used to their game and adapt and one should be proud but not arrogant about it, especially if one doesn't have a history of playing such players on a regular basis. The pride is just meant to encourage you to dig into your toolkit and figure out how to expose them. Arrogance just tells you you are the better player, but it doesn't explain how you should prove you are better.
The stroke below (windmill topspin) is a stroke I recommend people learn and understand, it has a good place if one is healthy enough to use it to follow the shape of the ball with power, as playing upwards can send the ball long under pressure. Here are some samples from the master:
For example, you made this shot, but this kind of stroke requires a precise ball read:
Here is a ball that you could easily have made if you have deliberately followed the shape and hooked it a bit more:
Here is a ball you should have hooked and gone up and down on. Play over the ball. Playing upwards will get you into trouble over time as you hit more and more powerful shots if you play close to the table or over the table.
Another thing - playing power backhands against weird spins is good if you practice it, but if you don't, you are setting yourself up for trouble. Use your footwork to get into position while a ball is in the air so you can play a good shot with your forehand. It is easier to adjust against the weird ball with the forehand once you have the right windmill approach. You hit quite a few good backhands with windmill technique, but it is not the norm.
You have to realize that these weird players, they struggle with heavy spin or extremely flat more often than not, so you want to load up the ball on your terms, not on theirs. I usually serve heavy backspin, let them push. and then slow open with heavy spin, extremely short, not trying to hit the ball past them, but trying to keep them at the table so their weird strokes are relatively ineffective and they have to make racket angles they are not used to making. Then I may throw in short topspin and sidespin as variations or short no spin, but they sometimes chop these pretty heavy so I need to be sure that the ball is high enough for me to hit through. Again, against the players, it is counter intuitive if you haven't played them, but spinning the ball short to keep the close to the table and keeping the ball slow is usually more effective than trying to blast the ball by them and getting it blocked or chopped back weird.
But for me, the biggest thing here is that you haven't lost to enough of these players to respect their game, I have, so I don't lose sleep over it, I just try to find strategies that make it more likely that I will contain what they do well.
. And the right knee is compromised so if you play me, you know where to put the ball 
