how much Improvment needed to attain pre rank shift rank?

I'm curious if to get back to the pre shift rank if you would need to improve much to get there again post shift E.G I hit a peak of MG2 right before the shift and went down the GN2 but now am at GNM with MG1 feeling quite a bit away but nothing that won't come with practice, if I were to get to MG1 or 2 again would I have improved significantly or only slightly?