You evaluate the position statically which only rarely works. As for your static evaluation you are correct, that the black bishop is stronger and that the pawns take some squares on the fifth rank. On the other hand, white has two active rooks vs one black rook.Stockfish gives a static evaluation for this position of +0.76 if white is to move and +0.5 if it is black's move. So statically it is roughly equal with a slight advantage for white.
However, such static evaluation is only really useful (if at all) in quiet and/or closed positions. In open positions like the one here, where there are concrete ideas, the static evaluation does not tell you anything. You should look at least a couple of moves deep to see what plans white and black could follow.
White has at least three obvious ideas: play against the a5 pawn, against the week pawns on e6 and f6 or directly against the black king.
Black has no obvious plan other than exchanging pieces and (if veryvery lucky enter the white position with heavy pieces.
Concretely to your question:
Black’s bishop has more scope than the white one: True, the black bishop has more scope, but there is not much to do along that diagonal.
White has some isolated pawns: Neither player has isolated pawns. Please check what an isolated pawn is.
the Black pawns rule the 5th rank.S: They cover squares on the 5th rank, but hey that's just the 5th rank, i.e., on the black side of the board (in the starting position the pawns rule the 6th rank....). Also (and much more relevant here), since the pawns are next to each other they don't support each other anymore and the pawns on e6 and f6 are weaknesses. Typically, building such horizontal line of pawns to gain space is a good thing to do in the opening phase, when the pawns can be supported by pieces. Towards the endgame such pawn lines can often become weaknesses.
Assuming it is white to move,my engine says about +3, (which means white is clearly winning) and gives the following line: 1. Rxd8 Qxd8 (or Rxd8 which is slightly worse) 2. e5
If black captures fxe5 or allows white to capture exf6, he will end up with a very weak isolated pawn on e6 (in addition to the weak pawn on a5) and a rather open king (ideas with Qe5, Rc7 or h5 look very scary for black).
If black closes the position with f5, the engine likes to go for the a5 pawn by exchanging queens with Qg5. Another viable option could be h5 with an attack on the king. In any case, black is left with weak pawns on e6 and a5.
So in summary, it is basically black's weak pawns that make the difference.
If in the initial position you...
- move the pawn from f6 to f7, the evaluation improves for black to +2, because the pawn structure is much more stable.
- remove all the pawns on the a and b files, the evaluation improves for black to +1 only.