If I remember correctly, 4...d5?! was considered dubious while 4...Bc5 and 4...Be7 were the main lines giving black easy equality.
Why not play a variation that does not give black easy equality at move 4?
4.Ng5 and 4.d4 are both more pressing moves.
Yeah. I only use 4. ... d5 against the quiet 4.d3 lines.
6...f6 is absolutely fine for Black. White should try to maintain tension in the center if at all possible, since taking results in a superior Black center (e5 pawn vs d3 pawn) when White is not ready to create pressure against it. White's plan must be to play O-O, Re1 and d4 but Black has time to make good moves in the meantime, e.g. ...Nb6, ..Bc5, ..Bg4 etc.
We should also consider lines like the following:
The idea is for black to castle queenside and play it like a sicilian yugoslav.