It does make it easier to dominate slams because everyone will play the exact same game on each surface meaning the top players will always win them. The differences are minor but they are mostly movement orientated for example Davydenko's horrendous movement on grass.
What it makes harder is for a surface specialist who excels on one particular surface i.e. a grass court expert or clay court dirtballer, to snatch his specialist slam title, or in general for a Thomas Johansson-style shock to happen. One of the key reasons for the ATP/Slams homogenising courts was cause they didn't want Johansson-type situations again. Not glamorous enough for them to make $$$$$$.
This. Unexpected champions don't make $$$. Last time we had a really unexpected Slam champion was Gaudio back in 2004 and we don't look like having another one any time soon - the closest thing that could happen would be Tsonga or Berdych taking a Slam.
Tsonga would actually have a very good shot at taking Wimbledon if the old grass was brought back, but with current conditions it's a very long shot.