It's not flexible in practice, because knowing the standard isn't optional. If you make the choice to not follow the standard, you're making the choice to write fundamentally broken software. Sometimes with catastrophic consequences.

I'm making the choice to pass pointers as void to get low-friction polymorphism. I'm making the choice to control the memory layout of my data structures, including of levels and type of indirection. I'm making the choice to control my own memory allocators and closely control lifetimes, closely control (almost) everything that happens in the system.

That has nothing to do with not following the standard.