It's not canon but in the original Battlefront II the 501st are preserved and become a more talented legion of stormtroopers than the regular rank & file called Vader's Fist.

It's never really been jarring for me. I've always attributed a separate set of rules for Jedi both young and old. Jedi are always at their best when they operate as peacekeepers but the Clone Wars is also not the first time that they've operated as soldiers. Many were soldiers during the Old Republic era. Maybe not nearly as many as during the downfall of the Republic but plenty all the same. There's nothing natural about Jedi. Their code, their insanely young starting point for training, their force sensitivity, their detachment while maintaining a caring and comionate way-of-being, divestment of all belongings. Many forget how rare force sensitivity is within the Star Wars universe. It's even rarer to be force sensitive enough to be brought to the temple. To be a Jedi that grabs the attention of the council? Only a few dozen ever do so in a generation...out of trillions of life forms that could potentially be Jedi. The Jedi have all this power at their disposal and they're aggressively taught to temper their actions with that power. Only after decades of training is it ok to explore the full potential of that power. It's a constant battle to keep the temptations of the Dark Side at bay. Add in being a soldier instead of a peacekeeper: Jedi operate on an incomprehensible frame of reference that is impossible to relate to. Even ing for the fact that Star Wars is fictitious, Jedi Padawans in war just doesn't shock me in a proportionate manner like child-soldiers in real life do. Padawans also always have a master at their side. Dulls the shock even moreso. I've been a Star Wars fan for 25 years so I guess I've just grown accustomed with the brutal realities that the characters go through.