You're jumping to conclusions.
I will not speculate on the current missing aircraft, preferring to wait for competent comment from the ATSB.
If, for US FAA registered aircraft....
From approximately 1961–1993, 24 aircraft crashed when spar failures caused the loss of the wing in flight. 35 more spars were found cracked during inspections.
Is the risk of catastrophic failure in Shrike aircraft further aggravated by the higher operating weights in Australia, those weights not being supported by the FAA and aircraft manufacturer?
Common sense indicates this may be the case, especially with ageing, high time, high cycle aircraft.
Modern forensic aircraft accident investigation has moved beyond the traditional "pilot error" cause and seeks to establish critical, contributory factors.
For those of you thinking this is an inflight break up, where is the wreckage, usually strewn over several kms ?.
That may be the case with high capacity pressurised aircraft but is generally not the case with non pressurised light aircraft.