When did you last crush your consumer camera?

Of course.
D600.
Supposedly lesser build, less magnesium alloy than the D700 and D800.

I have a D700. and D300 before that.
Both supposedly full magnesium alloy body.

Does full magnesium alloy really matter?
If so, how?

I once get a response that the non-professional build
get "flexes"/ "instability" in the body with a heavy lens.
Is that true?
The biggest lens I have is 70-200 VR II.

Is it true then that if one put a 600/4 lens (which I have no plans to buy)
on the D7000 or D600,
then, it does not hold up?

This is for normal consumer family photo use.

"I don't intend to throw the camera in desert, and come back in a month
to collect the camera."