That's the whole point.

The Maybach program was a complete failure. So instead of scrapping everything they worked on with the Maybach and rather than designing a brand new from the ground up S Class, they just rebadged the Maybach into the new S class.

I think in the back of their minds the board only approved the Maybach program when that, if it became that the Maybach program was failing that MB would use any of the resources it blew to engineer the Maybach for the new S class. SO that is basically why the Maybach looks/feels like an S class and vice versa. From the outset it was doomed to be that way, UNLESS the Maybach succeeded.