11% MFU does not mean 89% of GPUs are idle, it means that they're using the GPUs ineffectively.
The post you’re referring to doesn’t even include “89%” or “idle”. I’m not sure I understand the point you’re making then rebutting.
This might actually be worse from a power costs standpoint.
11% capacity is not 11% MFU. The first is about actually using the hardware for something in the first place, the latter is about how efficiently you compute. Different things.