You do know you sound apologetic?

Let's assume for a while that the mission was impossible.
That would be an even bigger failure than failing in a possible mission!

The top brass' job was to understand the limits of the own institution (to recognize that the mission is impossible) and to inform the political (civilian) leadership about its findings.
Said leadership surely insisted, but that's the moment when a non-failing institution would proceed to simply sacrifice its top brass one after one, as they insist on the finding.
They didn't for career reasons, and the army surely enjoyed all that growth in budget and numbers (all bureaucracies do) - and failed its nation by consuming a huge budgets, inflicting huge long-term costs, sacrificing lives and limbs and achieving close to nothing.

And you surely recognize that the alternative criticism above is not beyond the 3GW crowd's established repertoire, right?

The army cannot escape the blame for its failure; pointing at retired politicians doesn't deflect anything.