First of all I would like to say that 'aggresive margin" method of calculating players performance is very interesting, although the results are surface - dependent.
Let's assume that all matches are played on the same surface. Does "aggresive margin" method allow us to judge player's performance objectively? Well, it comes close to that, however it has got some drawbacks.
- it assumes that all point are equally important, which is not always the case in tennis; sometimes the player who wins less points than his/her opponent, wins the match,
- the value of 'aggresive margin" for a player in one particular match, depends not only upon the quality of performance [of this player], but also upon the quality of opponents' play,
- is there an objective method to tell unforced errors from forced errors?,
- points ending in unforced errors may be of very different quality