In Q2 2008, the Asian Top 15 stocks showed the best performance, whilst the European stocks were the weakest performers. However, this was more than compensated by a very strong absolute and relative performance for the Asian top-picks.
Do not hurry to make conclusion as for the correctness of the original; doubt first if you have correctly understood the jargons used. Though I cannot give a happy rendition of the sentence, I do not see anything problematic about it.
absolute and relative performance is obviously a fixed term that is modified by "strong"
It depends on what "this" refers to. It may be referring to the performance of the entire portfolio (Top Asian 15 + Top European 15+ Top US 15, compared to a target). In this case the sentence would make sense.
By "this", I guess the author meant the entire Asian market. Essentially, the author was trying to say that although the top performers in the Asian stock market is very impressive, the entire Asian market may not be that impressive. If this is the case, I agree that the author could have expressed it in a much better way.