You do not need to have the thumbhole that tight to not squeeze it. Are you not keeping your hand underneath the ball, or trying to project it too far out onto the lane? Are you remembering to relax your entire hand and let the natural movements of your arm/hand and gravity do the work for you?
Just so you have another example to base your experience from, I am picky about how the ball feels and have been fighting it for ages. I finally got something I like in the past few months. I even tried Magic Carpet, but did not like the feel of it very much. Since I have longer, skinny fingers with a decent sized span, I use 1/8" reverse and no lateral in the thumb, ovaled by hand to fit my thumb shape, and beveled just until I don't hang in the ball anymore. (Too much bevel gets me in trouble) I use Vise Hada tape on the back of my thumb to give me a consistent feel, and make adjustments in the fit with black tape (Frankentape is the greatest thing ever!), then use one piece of white tape for grip (tape placed toward the palm side of the thumbhole). The thumbhole is snug enough that I can hold the ball at my side with zero grip pressure, but it is also NOT so tight that I have to jam my thumb into the ball or anything. My thumb slides in and out easily if I put it in the ball without putting my fingers in as well.