A reader counters:
Your previous emailer who tried to minimize Federer's dominance is missing the point entirely. Quite the contrary to what he claims, Federer's amazing accomplishments are all the more amazing because of the fact that he doesn't have a real rival. And the reason he lacks a rival? Because Federer is so far superior to the rest of the current crop of players that none can emerge. How that complete dominance can be construed as a negative against him is utterly ridiculous. Should Federer purposely lose several majors to the same player, in order to provide himself with a rival, thus putting him in the same league as the other greats?
You could easily say the same about Michael Jordan or Tiger Woods. Both, at one point, became so completely dominant in their sport that they had (or have) no real rivalry. The gap between 1st and 2nd was so massive that neither ever gave another player an opportunity to become a rival, because a rivalry requires a measure of equality. Does that diminish Michael Jordan and mean he's not the greatest basketball player of all time, because he didn't have a Bird to his Magic or a Wilt to his Russell? Of course not. It was further proof of how great he was.
What your emailer is arguing is not about the greatness of individual players, but the greatness and entertainment value of eras. Of course you can argue that the Borg/McEnroe/Connors era was superior to the current one in terms of entertainment. Or that the Lendl/Becker/Edberg era or the Agassi/Sampras era were better for the game of tennis because of the rivalries. They were more exciting precisely because no single player dominated and there was always a good chance of one of the rivals beating the other. Seeing the same player win major after major in dominating fashion may not be exciting, but to claim that it diminishes that player's accomplishment or reputation is foolish.
Here's a YouTube of one of the greatest rallies of the modern era: 45 shots between Federer and Hewitt.