Only a small fraction of those 70% is memory management errors.
What do you mean? That 70% represents memory management errors.
70% are memory safety errors, a fraction of which are memory management errors.
Incorrect memory management leads to memory safety issues. That's what those words mean. You manage the memory, you get it wrong, you have a potentially exploitable memory safety issue. It sounds like you're just playing with words.
Fixing memory management errors fixes some memory safety issues, I agree with that, I only disagreed with your quantitative claim that you can fix all memory safety issues this way.