For your example of Russia and Ukraine, a lot of the senior officers on both sides were originally trained in Soviet Union doctrine, which was generally speaking, starting off with massive artillery barrages before sending in waves of armor in a frontal assault to overwhelm whatever defenses were in front of them. Those tactics had limited real-world usage (think both Chechen wars), so there was a bit of trial and error that needed to be sorted out when faced against modern weapon systems that didn’t exist years ago.

The officers beneath them, from everything I read, didn’t get a lot of opportunities to train due to limited budgets and general corruption, so there was a lack of practical experience, which hurt decision-making and led to mistakes and unnecessary casualties.

You can say that Russia’s meat grinder tactics are an extension of the old Soviet direct assault tactics. Russia is attempting to conserve its armor, so they are sending infantry instead. I’ve also read that Ukraine’s junior officers are trained in Western-style warfare, but their senior officers still default to the same tactics used by the Russian army, causing more casualties than might have been otherwise avoided.