In biology terms, natural selection favors players with more extreme grips. Today, baseliners are the surviving species and the pure serve and volley players have died out. Topspin shots are replacing flat and slice shots. Eastern is no longer the dominant grip. I am not saying that western is correct or eastern is correct, but as of right now, players are leaning more towards extreme grips. I am pretty sure that no top 10 player uses an eastern grip for their forehand. Federer is extremely talented and manages to do well with an extreme eastern. Most players use semi-western now. More juniors are beginning to use western grip on their forehands. This is at least what I notice in the US, now if we move to Europe and especially South America, eastern grip is virtually non-existent with clay-court specialists.