I think one of the major changes in the pronunciation of Greek was the shift from a system of distinctive syllable quantity (heavy and light syllables), with a mostly independent pitch accent system and no contrastive stress, to the modern system of contrastive stress and no distinctive syllable quantity or pitch accent. Given that this shift was already well under way in the Roman period, I can certainly see the advantages of using the modern pronunciation, rather than the Erasmian, if you are forced to choose between the two.
The disadvantage of the modern is that, for example, you fail to render all sorts of vowel contrasts that still existed in Koine of the time, e.g. the contrasting vowels represented by iota, eta and ypsilon, which are all pronounced "ee" in modern Greek but were still distinct in Koine.