1. he's not playing 2600s
2. just said his opponents were playing this, not him
smyslovfanatic is just used to people asking questions like this, and answered an entirely different one, didn't even bother reading.
lol
I'm really not sure how playable it is in this move order.
I have ~50 games between players rated +2600 in this opening, and the vast majority are rapid/blitz/blindfold games. White wins a staggering proportion of these games, even at higher levels.
if you want to play the Philidor, I think you need to find a different move order.
There is no REAL problem, other than 3.d4 Nf6 4.de5 Nxe4 5.Qd5. In practical OTB play white has a slight advantage at no risk, but in correspondence play I'm pretty sure I would give it a miss and go for the main lines, as white's advantage in that line is quite manageable.
There are a few 2600+ players, like Bologan, Nisipeanu and Bauer who have used the Philidor at regular games with good results- so it's safe to say that this opening is quite OK.
thanks everyone for the help!