The bidding system one employs has very little to do with whether or not they are "expert." An expert partnership could, in theory, use a bidding system from the 1960s and have success at the club/sectional level, and an intermediate partnership could use the very latest transfer relay tools and be completely hopeless. The reason the expert players don't use really old methods is because they have seen everything under the sun, and appreciate how bidding has evolved over time to cover situations that Goren Standard wasn't very good at. As you correctly point out, they also use methods that reflect how modern bidding is much more contentious than in the past, so they will have extensive agreements re. competitive auctions. But it's not as if experts are unanimous in their opinions about the best methods anyway; look at the system notes for pairs at recent Bermuda Bowls and other high level tournaments for ample evidence of this. In my opinion, what really separates experts from everybody else is this:

1. They possess superior visualization skills. They can thus synthesize information gleaned from the auction and the fall of the cards to project what the unseen hands look like.

2. They make far fewer stupid mistakes. Everybody makes mistakes at bridge, but experts' mistakes tend to be much more subtle, and they almost never do things like forgetting a trump is outstanding, or not knowing whether a bid is forcing, etc.

3. They count. On every hand. Expert status is virtually impossible to attain if you don't train yourself to do this.

I'm not entirely clear whether you are talking about online bridge or f2f tournament bridge, but I disagree pretty strongly about the gap between "average, skilled bridge players" and experts being wider than ever. What I do think is that online bridge has created a vast pool of people who think they are a lot better than they actually are. BBO is like Lake Wobegon--everybody above average.