You're not wrong, I've seen this in a few cases - I guess I'm looking for some examples from guys who actually have a 5012 unit and what they have done with current battery tech. As you suggest, dropping one cell is an option, or to make things uniform, drop two cells to10S. Probably the best option is to substitute a modern ESC, and go with 12S for all out performance. The heat sink centre body appears quite substantial, so I'm guessing that the 1521 Neu motor should cope with a modern 12S system...
Regards, Frank