I prefer not to hit with a lot of topspin but i CAN generate enormous amount of topspin with an eastern forehand if i want. Sometimes i'm even surprised how i do that but sometimes the ball jumps over the head of my friend and he just can't hit it. The reason i don't use it is, i need to hit with a lot of power to make it an effective weapon against better players but i'm not ready yet for it.
I will try to explain my forehand. First of all, you and your wrist need to be loose, otherwise you loose all the effect. I push the racquet with my left hand in a natural position and i pronate my forearm in a way that the racquet face shows the ground and the tip is towards somewhere between net and side fence. I let the gravity make the drop and when the racquet drops, i supinate my forearm back so the racquet goes back. The supination is started by the shoulder turn mostly, so it is a natural motion. I hit through the ball but i get a little under the ball so it gives you the net clearance. When i make the contact, i pronate my forearm again to give some extra spin to the ball and finish the stroke in a ww follow through.
So i don't listen to anybody who says it's impossible to hit heavy topspin with an eastern forehand. If you use it in a traditional way, yes it is very hard but with some practice, you can learn the pronation-supination-pronation route. I used to have a semi western forehand but i like hitting topspin with a relatively flat trajectory, so turned to an eastern forehand.