Discussing which era is stronger, etc, is completely pointless, as there are myriad factors that you can't ever possibly take into consideration. Furthermore, it's impossible to say when one era ends, and another begins.
In addition, there is this weird and obviously self-serving revisionism on here that great players from the past couldn't play! For example, Hewitt is often spoken about as if he wasn't any good, but he beat Nadal in four of the first five matches they played, he beat Federer consistently in their early encounters, he had a winning record against Sampras, and a 4-4 record against Agassi. Djokovic only faced Hewitt after he was outside the top 20 in the world, but he was still spanked the first time they played, and Hewitt pushed him very close at Wimbledon in the second meeting.
The way you hear people talk on this site, you would think the likes of Hewitt and Safin were useless. Hewitt was a brilliant player for several years, and Safin was intermittently awesome. He played one of the best matches ever when beating Sampras to win the US Open. The difference is that they had a much smaller window of peak performance, and struggled with persistent injuries. On their day, at their peak, they would beat Federer, Nadal, or Djokovic quite regularly. Arguably, it's tougher to face them at their peak than a 38 year-old Federer, for example.
What the top three today have delivered is persistence, consistency, and longevity, while they have also been fortunate with injuries and have benefited from increased understanding in training, diet, etc. The way certain people go on about them on here, you would think they could never possibly lose a match to anyone except each other. If Djokovic can be beaten by Cecchinato, he can lose to many, many clay courters from 10-20 years ago. If Nadal can be beaten by Dustin Brown, he can lose to basically anyone on grass! If Federer can lose to Millman, he can be beaten by many players from the past on a hard court. Rest assured.
