Nothing has changed, there have only been a handful of guys to watch in every era, the rest has always been rubbish to me.
There are times when there are a lot more major winners. 1996 to 2003 for example. There were 32 Titles and 17 different winners. Sampras won 6, Agassi won 5, Kuerten won 3, Hewitt and Kafelnikov each had 2, but every one else won just once (that includes Federer's 1st in 2003).
In the 48 Grand Slams since then however, Federer, Nadal, and Djokovic have dominated winning 40 of the 48. Only Gaudio in the 2004 French (before Nadal), Safin at the 2005 Australian, del Potro in the 2009 US Open, Cilic in the 2014 US Open, and then the 2 from Wawrinka (14 Aus, 15 Wim) and Murray (12 US, 13 Wim).
Even pre-96, Sampras won a lot, but he had not real consistent competitor winning majors and Sampras really only dominated on grass.