Strictly, ace count doesn't measure serve quality directly, as a player also needs to win matches in order to have more opportunities to hit aces, and therefore he needs a strong game besides the service. Aces per match, or aces per serve point would be a better statistic.
Yes sure, Ivo playing so many matches on the tour like John and Milos wold be 3rd 1000+ aces guy, but my point was in 2012 season John and Milos were arguably best servers on the tour and that both have 1000 ace season is great that their prooved themselves that they did it. Ivo´s serve declined he is probably 3rd best server after them. Others are not even for discussion best server in the world.
BTW Ace-per match ratio is very used, but it is very misleading, because it depends on how long matches are, or how many service games you play and so on. Most accurate ratio would be ace-per 1st serve IN - i am using this by myself, but also it isn´t 100% accurate, because guys like John or Milos have also some 2nd serve aces - % of total number is low, but still it can´t be 100% accurate number, because of this