I had frustrations with the Witness too, but I think that's expected with great puzzle games, and overcoming them makes the rewards even greater. I had no idea about the drag mechanic! That sounds so nice. I'll give it a try.
I think maybe the tutorialization needed to get across better that the number had to be in the shape, and that it did not need to be in the center. Additionally, I think the first two 7 puzzles might have required the same solution, which was a bit confusing and didn't get the symmetry point across to me to me. Maybe if that first 7 puzzle had the 7 at the top or off to one corner? I'm not sure. Or maybe introducing early a grid that couldn't be symmetrical at all, like a 5 with only 5 squares.
Regardless, the game was spectacular. I was very impressed with the amount of puzzles you were able to get done.