I analysed the game. 5...e6 stands out as a particularly bad move. The few times White's system has been tried in games involving +2300 players, Black has played 5...Nc6 which develops and maintains black's flexibility.
Here's my analysis, helped along by Firebird at the end. (All mistakes are my own.)
[Event "?"]
[Site "?"]
[Date "????.??.??"]
[Round "?"]
[White "Enter New Game"]
[Black "?"]
[Result "*"]
[PlyCount "45"]
1. c4 c6 2. Nf3 d5 3. cxd5 cxd5 4. g3 Nf6 5. Bg2 e6 $6 {I don't understand why
a Slav player would voluntarily incarcerate his own light squared Bishop. 5...
Nc6 followed by Bf5 makes far more sense to me.} 6. Nc3 Be7 {Again, I prefer
Nc6, leaving open the question of where the dark-squared B will go.} 7. O-O O-O
8. a3 a5 {This feels like a knee-jerk reaction. I don't know that b4 and Bb2
was such a scary proposition for White. It seems that Black is so afraid of
white's possible development that he neglects his own plans. Firebird
considers 8...d4 to be best.} 9. d3 {even better was d4, and white has a nice
type of Catalan position.} Na6 {Yeah, the Na6 ideas are common to many
openings. But here, with the e6/d5 pawn structure, it lacks any bite. I don't
see the plan connected with it.} 10. Bf4 Bd7 {Perhaps Black should play Nc5
immediately here. His maneuver with the light squared B lacks conviction.} 11.
Ne5 Be8 {Why would Black play Be8? He's made a terrible bishop out of his
light-squared B, and a trade on d7 would only remove Black's (self-inflicted)
bad Bishop.} 12. e4 $5 {White's play has been nicely consistent. But now may
not be the time to open up the center. More consistent was e3, Rc1, and slowly
increasing the pressure. This hasty move gives black some counterplay.} d4 13.
Ne2 Nc5 14. b4 Ba4 $1 {I missed this when I was analysing without an engine.
It's amazing, but the B which was doing nothing has come to life. Black's
position is still difficult to play. I think White still has an edge here, but
both sides will have to play creatively to gain an edge.} (14... axb4 15. axb4
Ba4 16. Qb1 Ncd7 17. Nf3 {And White's pieces are all active in the center.
Firebird considers this position almost equal, but White's play is much easier.
}) 15. Qb1 Nb3 16. Ra2 Nh5 (16... Nd7 $5 17. Nf3 g5 $1 18. Nc1 $1 {Again,
Firebird's discovery.} gxf4 19. Nxb3 Bxb3 20. Qxb3 fxg3 21. hxg3 Qb6 {And the
position is about equal.}) 17. Nf3 Nxf4 18. gxf4 axb4 19. axb4 Qb6 20. Rb2 Bxb4
21. Rxb3 Bxb3 22. Qxb3 Ra3 23. Qc4 *
NOTE: It appears that my recommendation, 12.e3, runs into h6 intending g5, which gives Black counterplay. Instead, simple 12.d4 (which could have been played in one move) retains White's advantage.