Don't sweat it. Beating a machine is not a normal thing in my opinion. At least on the newer ones. You can only beat them if you play really really good and have the pin down to the last inch inside of your head. If this is not true I might just simply suck too.

I started playing 3 years ago and I'm still progressing and feeling it. I can't imagine that you already reached the ceiling. Also don't expect to have a big game everytime. Watch some really good players play on twitch and you see that sometimes they got shitty balls and bricked shots too.

The part where I really feel the improvements I make is in ball control. It is the absolute ultimate skill along with precise shots. Bounce pass, tapping passes, post passes, drop catches and live catches as well as beginning to feel when to nudge the machine to keep it from the outlanes (ideally you want to hit the ball with your upper side of the slingshot and get it away from the danger zone).
If I play with my gf this is why I win almost everytime. She hits the shots but can't control the ball enough. If you got the ball on your left flipper and need it on the right you have to have a method to get it to the right and be comfortable that it works.

My advice: Keep playing and watch other good players play. Watching others helped me tremendously.