This is my 4th season and I'm only starting to go down blues and easy blacks with confidence. My first three season was a combination of bad fitting boots, bad technique and overthinking that resulted to frequent cramps in legs and feet that puts me in a backseat sking position.
Getting the right fitting boot and a boot fitter that stacked me in a neutral stance helped a ton. I instantly felt a lot more confident going down steeper areas starting with my skis pointing downhill. But I always have to stop at the top, position myself, take a deep breath and go... I was never able to ski from top to bottom without stopping.
My light bulb moment came when I started to practice proper pole planting. I was convinced for a long time that I don't need my poles to learn how to ski properly. So I never paid any attention to my poles when I'm going down the mountain. They are just there to help me move forward on flats. It's complicated enough that I need to pay attention to what's going on with me feet, legs, body position, arms etc... I'll just deal with pole planting once I mastered proper skiing with my legs and feet.
Here's the thing though, once I started to practice pole planting... everything just clicked and felt natural. I am able to keep a good rhythm from top to bottom and skiing became less of an effort all of a sudden. I was able to ski down steeper parts without stopping and I was able to go faster without feeling like I'm out of control.
In retrospect, I now understand why proper pole planting helps beginners like me learn the proper form. I noticed that pole plant actually forces me to pull my body forward right before the next turn, forces me to 'reach downhill' into the proper position, and provides that micro adjustment for me to stay stacked and in control for the next turn. My husband said I skied like a different person because my movements suddenly became natural. Since I was focusing a lot on proper pole planting and timing, I wasn't over thinking my legs, feet, ankles, skis edge, skis together, body position etc... my turns are no longer forced.
On the groomed piste vs soft snow/powder conditions, I think you might want to check your skis as well. I used to have a beginner skinny on piste skis - they are chin level in length and pretty narrow (70mm). These skis are for beginners because they are easier to turn. I find myself feeling wobbly at certain speed and I struggle to turn in soft snow, crud or powdery runs on those beginner skis. This season I tried a pair of longer and wider all mountain skis (they are as tall as me and 90mm wide) and I instantly felt the difference in terms of stability and control. There are less 'oh sh*t, oh sh*t' moments when I go through some bumps or feel a block of ice beneath... they are more 'ooops... oh well' moments now.
Lastly, I fell a lot learning how to ski. As in almost every other turn... and I still do (especially when I accidentally ended up on a black mogul). What helped me overcome fear is that I got really good at falling down properly and get up. It takes some mental commitment to convince myself whenever I'm out of control to stop fighting the fall and just go down, stand up and reset. Since I'm comfortable with falling... I am able to push myself to try steeper terrain, bumps, jumping etc... I would tell myself: "Worst case, I fall". :-)
TL;DR: Good fitting boots helps with proper stance to start with. Pole planting helps with rhythm and staying stacked. Longer wider skis for crud and powder... Lastly, practice falling and standing up to build confidence.