Firstly, we did not have pre-selected and well-trained commanders of fronts, armies, corps and divisions. The fronts were led by people who failed at one thing after another (Pavlov, Kuznetsov, Popov, Budyonny, Cherevichenko, Tyulenev, Ryabyshev, Timoshenko, etc.)
Under-studied and untrained people were also assigned to the armies. It could not have been otherwise, since there were no candidates for the fronts, armies and formations trained in peacetime. They didn't know people well. In peacetime, the People's Commissariat of Defense not only did not prepare candidates, but did not even prepare commanders to command fronts and armies.
The situation was even worse with the commanders of divisions, brigades and regiments. Divisions, brigades and regiments, especially second-rank ones, were given to commanders who were not suited to their task.
In short, each of us knows the consequences of the command of these people and what our Motherland experienced by entrusting its fate into the hands of such leaders and commanders.
Conclusion: If we do not want to repeat the mistakes of the past and want to successfully wage war in the future, we must, sparing no expense, train commanders of fronts, armies, corps and divisions in peacetime.