Claycourter Chang with 77% ranked 2 in 96 ?
Then Rafter 69% ranked 2 in 97
Then some guy called Rios without a slam ranked 2 in the year end in 98??
Kafelnikov with 65% ranked 2 ahead of Sampras in 99
Then Safin and Hewitt who were like 19-20 quickly rose because these guys quickly got outdated? String Technology cannot cause such a big change that these veterans failed to adapt, these veterans were all crap all along .... Compare that to someone like Lendl who had so many years when he was above 90% in win % for the year, Sampras never even came close to 90..... How did rios without a slam become 1? This was a weak era for sure as
@mike danny pointed out once on Sampras not having as good competition as Federer or Nadal, this is true.
Tennis continually evolves. In the mid-'90s, there was very clearly a significant increase in the depth of the men's tour. Guys like Kafelnikov, Rios, Moya, Rafter, Corretja, Albert Costa, Kuerten, Mantilla, Rusedski, Henman, Philippoussis, Berasategui, Enqvist, etc. all emerged around the same time. That list alone includes several wildly different playing styles and strengths and weaknesses. Those guys joined the established guard of Sampras, Agassi, Becker, Edberg, Courier, Muster, Ivanisevic, Chang, Bruguera, Stich, Krajicek, Ferreira, etc.
For those who followed the tour closely back then, it was pretty exciting. Sure, Sampras was the best. He was favored in many non-clay tournaments that he entered. But outside of a few utterly dominant stretches, he was beatable and he did lose.
The stylistic variety and varying surface speeds and conditions from tournament to tournament created much more parity. Seeding only 16 players at slams also occasionally created very disparate draws for top players. Each surface had leading candidates to hoist big trophies, but you wouldn't have been surprised had one of about 10+ players triumphed.
Towards the end of the decade, Haas, Safin, Hewitt, Ferrero and Federer among others showed up. By then, much of the old guard had retired or faded from regular top contention. The new crew started to raise the level of play ever so slightly again.