and gearsets dont fail because of housing flex.  they  fail because the ring gear deflects  ( has nothing to do with extra ribs on the housing)  and they murder themselves.   trucks with v6 thirds eat themselves just as often as 4cyl housings.

uh! and the ring gear deflect because of what 
It has been proven that the extra ribs on the side of the third member is a major improvment strength wise. the ring gear deflect
 because of the third member deflecting. I didn't say the housing was flexing.
beleive me or not I've never seen a rear axle tube nrak like yours, and if you ask me, I think it's due to other thing then strength issue.