That's the thing though, that's part of Reika's license for DragonAPI and its constituent mods. There can be addons, so long as said addons don't harm the internal consistency of his mods, so long as you don't tread on his toes, basically. What you propose would harm the internal consistency of RotaryCraft, and would likely effect ReactorCraft, as well, since said ore multiplication makes getting into the mod less of a chore, and may well even be nigh-essential once you get around to designing a fusion reactor, because of the absolutely insane amount of magnetite you need to get the thing built up.
Honestly, I agree with Reika's position. I make the mod, then I or my team are the ones that controls the destiny of said mod, unless I open source it. If I made a stand-alone mod, then I would have a very explicit clause, much like Reika's, that would forbid any addon or mod author from altering said mod's internal mechanics in any way, shape, or form. They can utilize said mechanics all they like, but I balanced the mod the way I did for a reason, and people hacking into it to change things about could end up fudging the entire thing. However, I would of course be open to balancing suggestions for the mod itself.
Like it or not, RotaryCraft is a standalone mod. It has some bits for inter-mod compatibility, but it doesn't go out of its way to adhere to anyone's idea of balance except Reika's. Greg's idea of balance is fundamentally different, and likely anathema to Reika's, making the two incompatible. Once again, to put it extremely bluntly: if you don't like the way RotaryCraft handles ore multiplication, then don't use it. No one is forcing you to use his mod's content over Greg's. If his is superior to Greg's in the modpack's environment, then...well, again, don't use it if you don't like it. Or, alternatively, you could lobby your modpack creator and/or server admin to remove RotaryCraft in favour of GregTech because one may imbalance the other. However, if you take that route, I advise you to be prepared to hear a lot of laughter at your expense, assuming the modpack author and/or admin aren't your friends.