I would disagree on that Gerrard and Lampard comment mate. That said I don't really consider Lampard a central midfilder more an 8 and a half with drawn or a 10. He did have tackling and tracking back responsibilities though this area of his game is completely overlooked he largely played under coaches with rigid defensive systems. I think Lampard wouldn't have thrived in historical football he was lucky to have played in an era were football systems developed beyond 4-4-2 he wasn't very creative at all. I think your wrong on Gerrard I think he had a huge defensive responsibility throughout his career and was a very disciplined player, he played many posititions that required broad skill sets both creative and defensive he was a very balanced footballer both defensively and creatively.
Have to say I think your completely wrong, Barkley was told he was the best player in the world by Martinez and told to play were he liked the semi vs Utd last season typified that to me he was awful and a passenger, it was like having 10 men. He didn't influence games, the tempo and got a goal or assist in one of five games that looked good. Koeman has brought him along to the point now that he can influence every game, I don't think he is the finished article in the role he's playing and I expect him to reach a greater balance and effectiveness in his game but he is now progressing and developing for the first time since his breakthrough. I think He really suffered under Martinez and got exactly what he needed under Koeman I.e. A boot up the backside.
In terms of his best season it's what you value, a goal and assist in one in five game and being a passenger for the rest isn't good. Being effective in 38 games is better and the rest is good. Your also jumping the gun a bit there is just over a quater of the season to go yet.
It's an interesting point though when you look at the squad under Koeman who has progressed under his coaching from last season, Rom, Coleman certainly Ross for my money certainly.