I have seen lots of famous, success coaches such as Lansdorp, Macci, Dave Smith and others saying that when they are first teaching the groundstrokes, they think the eastern grip is a fine grip to learn with. The eastern grip allows you to get the feeling of contacting the ball cleanly and hitting through the shot. It's a somewhat simpler stroke than the modern atp forehand. Later on in development, players may experiment with slightly more extreme groundstrokes grips and turning the hand over and finishing around the body on the follow through, after they have already learned how to hit through the ball with a basic grip.
Too many people try to copy what they see on tv, before learning the basics. If you can learn to hit a clean predictable Tracy Austin type groundstroke with a long, follow through out towards your target, that is enough to beat 99 % of the players at your local club.
A common problem for juniors is the ball bounces up so high for them that an extreme grip feels more comfortable, but if the grip they learn with is too extreme as they grow in height, they will be stuck with their extreme grip and won't know how to hit through the ball.
One of the best guys I hit with was a nationally ranked junior player who learned with an eastern grip and catching his follow-through out front. As he progressed he shifted his grip over to what would be called either an extreme eastern grip or a semi-western grip on these message boards. I asked him about this topic the other day, because it intrigues me. He said he feels learning to hit with his hand behind the racket and driving the ball helped his groundstroke development.
I know excellent players who learned to drive their groundstrokes with continental, eastern, semiwestern, and extreme western grips. On the groundstrokes, there is some freedom to let individual style and preference take over.
I know there are coaches out their who think players should start right away with a semi-western grip and an open stance.
I know plenty of good players who started off learning a basic topspin drive from closed stance, or a semi opened stance, or neutral stance or whatever it may be called. Starting with an extreme open stance right away is tough because some players wont turn there shoulders and coil properly.
I personally learned to add and subtract before I learned multiplication and division. But, to each their own.
Look at youtube videos of Carolyn Xie, she hits what posters on this board would probably call "modern strokes". However, if you look at her background you will see that she is a Robert Lansdorp protégé who started off learning that driving through the ball is one of the basic fundamentals of the groundstrokes.
Modern strokes are great, but a basic topspin drive is all you need to beat everybody at your local tennis club.
Every day there are threads on here where people are claiming that Pete Sampras's forehand isn't modern enough, or that Ana Ivanovic and Serena Williams follow through too high on their groundies. These claims might be the norm on the talk tennis message boards, but in real life I think most skilled instructors and players only laugh at hyperbolic claims of this sort.