You can't compare. Balls have changed, laws have changed, boots have changed, pitches are completely different. Odemwingie would struggle playing with a leather ball on a muddy field, equally Astle would probably struggle to keep a modern football below the crossbar and defenders of the 50's and 60's wouldn't last 5 minutes before being sent off.
Realistically though, modern players are fitter, train better, and have more competition to get to the pinnacle of the game. Nowadays there's far more people in the world, far more people playing football, and where a person is born has virtually no impact on their chances of playing professional football. I think the ability of the average pro is far greater than it would have been 50 years ago.
As for Albion's greatest, you'd have to compare based on what the players have done for the club. In that respect, there's not many modern players who would make our all time XI. We have great servants like Brunt and Mozza, but they've won nothing, and if we ever have an exceptional player pass through the club the chances are they won't be here long enough to reach 'all-time great' status. Foster is probably the only one, an almost world-class goalkeeper who stayed for 7 years because of his family ties to the area.