I find the hole and the plug to be the oddest aspects of this.
If it's OK to have a hole; and I am not sure that it is; then why plug it when this can result in crevice corrosion and the plug material is a quarter of the weight and therefore brings no benefit in rotational balance.
Then there is the question of "Hot spots". Are these related to the presence of the hole? One might expect them to be.
If there is moisture that can promote corrosion, and there is a hole, then surely the hole is a potential escape route for moisture (hone and polish?). The question that then arises is where would the moisture go after that. Is that the reason for the plug?
Not simple, whatever way you look at it.