You know I was just in the process of crunching those numbers myself? It seems to me that the only comparable weaponry the Covenant have to a standard Imperial Lance battery are the Energy Projectors aboard their Super Carriers. And as you pointed out, Void Shields are designed to prevent those same lances from reaching the soon to be gooey starship exterior hull plating.
Look, I'm trying to be polite here, and while I'd love to weigh in on that discussion, it really is the kind of thing for another thread. I'm much more interested in a conflict specifically between the Imperium of Man and Covenant, sans all other factions in their respective universes actually entering said conflict.
If you like, I'll create that thread for you and we can engage in that discussion there.