I don't think anyone would argue fields are deeper now than when Nicklaus was playing. So it logically follows that if there are more players capable of winning a random tournament, then the number of tournaments top players would be expected to win would come down.
So it's not Tiger that is necessarily taking tournament victories away from the likes of Mickelson, Els, and Furyk. Rather its there are more random guys capable of winning one tournament and/or major by having a completely ridiculous week.
Also David Duval is a perfect example of the slightly less than great all time players who seem to be more prevalent in Tiger's day. Tiger and Phil have both now been great golfers for about 20 years give or take. During that time frame, guys like Duval(13 wins in 5 years), Vijay Singh(great career, but 13 wins in about 1 1/2 years). Padraig Harrington won all three of his major championships within about 13 months of each other too.
Maybe there were spurts like that from players in Nicklaus' day too, but it seems more common now than 20-30 years ago.