High aggression factors

[Gyre]

I have a friend of mine who recently started playing PP's 3/6 6max game, and over all his quite new to short hand play.

So far he is running good and beating the game quite nicely over 5k hands. But his aggression factors are very high. This is what i looks like:

Aggression
flop: 5,51
turn: 3,84
river: 1,70

I told him that he is majorly overaggressiv but he responded that there is no "perfect" stats to strive for and that this high numbers might fit one players game while lower aggression fits other stiles of play.
I dont realy buy that, and personally i think he is losing value whit these stats, but I dont have any good arguments that so is the case.
Why is it better to have like 3,2,1.8 stat then my friends 5.5,3.8,1.7?