Quick Note: This ask got lost in the draft folder; it was a follow up to this question about superheroes.
No. There’s a huge difference between someone standing post, and someone who jumps rooftop to rooftop every night, brawling with any petty criminals, and wandering supervillians, they come across.
In my opinion, for a royal guard, you’re looking for two things: excellent combatants, and almost more importantly, loyalty.
Because your royal guard will be elite forces, you can afford to outfit them with the best, or better than the best equipment. You can afford the most demanding training.
When these guys go toe to toe with an untrained mob, as a unit, they’ll wipe them out.
There are a lot of ways to engender loyalty, ideally, even guards who can no longer serve because of physical limitations should be at least cared for, if not kept around as security advisers and in other leadership capacities.
Now, I did say that was “in my opinion.” History has certainly showed enough cases where the palace guard were treated terribly and replaced constantly, to avoid letting them rise up in rebellion, or to become the true power behind the throne.
For every Secret Service, there’s a Praetorian Guard or cadre of Boyars, waiting to call the shots. So, this is a real danger. Rotating through the guard as viciously as possible is one way to handle that threat. From what I know, it’s not an effective way to prevent a palace coup, because you end up with a lower caliber of less motivated soldiers as a result. But, ultimately, that’s a world building question.
To a larger extent, this also applies to your nation’s military as a whole. Do you want forces that are too fractured by internal strife to turn against you, or do you want a unified elite force to deploy against any foe, with the belief that they will love you.
It’s the cruelty versus mercy question from Machiavelli’s The Prince; is it better to be feared than loved? Which is more appropriate? Which suits your story, and your setting, better?