I usually play the queen's gambit with white and the french defense with black. I just noticed that a common position of the pawns for white with the queens gambit declined is c4 d4 e3 and with black with the french defense the pawns are usually on c5 d5 e6. Also, there are usually knights on c3 and c6. In this aspect the french defense is basically the mirrored version of the queen's gambit declined.
Would you agree with this? And in how far can I play the queens gambit the same as the french defense? Because if the french defense is a good opening then surely playing it with white would be even better as you have an extra move since you start.
I disagree. In the french defense, white gets pawns on d4 and e4 - this creates a totally different situation from QGD.
You're making the common mistake by looking at your pawns only. There are 16 pawns on the board, and they determine the pawn structure. So although the French and QGD superficially look similar, they are very, very different games.
With the French, you have pawn chains on d4-e5 up against f7-e6-d5. White is generally looking at f-pawn breaks and kingside mating attacks, and Black is looking to bust open the pawn chain with c-pawn and f-pawn breaks and counterplay on the queenside. With the QGD, black may have a similar pawn structure, but White has played d4 and c4, and usually only plays e3, hoping for a later e4, and you can end up with a few different types of pawn structures once it resolves. This will mean different outposts, different pawn breaks, different files that open and need to be controlled, and a different flavour to the game. You have to look at what's actually on the board and make your best move based on that.
There is one rare line in the Slav-complex that can lead to a mirror of the French. 1.d4 d5 2.c4 c6 3.Nc3 e5 and if now 4.e3 e4 we have indeed a French anvanced with reversed colours. You see Black goes e5 here, but in the classical Queen's Gambit the pawn is on e6, so nothing similar to the French is likely to happen.