You've answered it yourself already, it didn't feel comfortable to you. Why jeopardize your entire game just to play like someone else? It's perfectly OK to deviate from your coaches.
Since you already have a semi-western grip, there's nothing you can do with an eastern that you can't already do with a semi-western.
The notion of "easy power" really means a flatter shot, which you can already do with a semi-western.
Also, a change to certain grips doesn't mean you'll advance to another level. Changing grips changes a lot of things, your footwork, your swing path, and most importantly, your contact point.
I have an eastern grip, and I wouldn't advise anyone to change to it for the same reasons I won't change to a semi-western.