So it looks like with this method, if a journal publishes more papers, this will give it more of a chance to boost its h5-index? This probably accounts for the high level of arXiv, and PLoS One beating out PLoS Biol.

One problem with impact factors is the way that a few articles can account for the majority of citations. For instance, a bioinformatics method that is widely used could attract thousands of citations, boosting the impact factor of the journal by a few points. This method doesn't solve this, as it expressly focuses on the top n articles and ignores the impact of the remainder. For instance, PLoS One's score of 100 is because the top 100 articles got 100 citations - it says nothing about the distribution of the rest.