I wouldn't say the Eagles have a better roster overall....I just think they have a more wisely constructed roster and team building philosophy....which was instilled by Andy Reid, and taken as gospel by their owner ever since.
In this day and age....you can't be good everywhere, due to salary cap. You have to prioritize. Andy is famous for saying "Give me a Quarterback 1st. Then give me TWO offensive tackles. Then give me TWO pass rushers. I'll fill in everywhere else as we go"
Over the years...Philly always lived by that...and now the Chiefs. Philly went the extra mile to always make sure they had a Top 3 OLine at all positions for last 20 years...and dumped tons of resources into DLine... Chiefs too.
Then when it comes to LB or RB or secondary.....they find bargains, and hope their superior lines cover them up. Right or wrong...they have a plan....supported by their owner.
We are more scattershot: Hey LB in rd1 this year, RB in rd1 next year, Wr rd 1 next year...then CB....then guard...etc. it's kinda random.
Philly will spend a rd1 pick on an OTackle, a Dlineman, a QB, occasionally a WR....and that's it. So their talent is same as ours...but it's concentrated in the most high impact areas: on the lines, QB, receiver.
Ours is more spread out. I think how they constructed their team gives them slight advantages over similarly talented teams that have more random team building philosophy...as evidenced by the fact that they've now only lost 3 games in the last 2 seasons combined ,including playoffs and superbowl, that they've tried to win when hurts played.