This is honestly such an oversimplification of what happened that it completely ignores the episode.
First of all, "Kara was executed for attempted murder, not magic" is only true if you deliberately erase all of the context surrounding why she was in that position to begin with.
Kara is a Druid. She belongs to a people who have spent decades being hunted, imprisoned and slaughtered by Camelot because of Uther's anti-magic regime—a regime Arthur has continued. By the time we meet her, she's lived her entire life as a fugitive. She has every reason to see Camelot as the enemy because Camelot has been the enemy for her entire life.
Arthur and the knights don't find Kara wandering around looking for him to kill him. They track her down after she's already been injured. She's alone, exhausted, bleeding, hiding in a cave. Arthur arrives in full armour with armed knights. She's cornered. There is no escape. There is no equal fight. There is no premeditated assassination plot where Kara set out to murder the king. She's a hunted woman backed into a corner by the people who have spent years hunting people like her.
She lashes out with a knife when she's surrounded.
Calling that "attempted murder" as though it's equivalent to someone calmly planning and carrying out an assassination is such a bizarre way to describe what actually happens on screen. It's a desperate act from someone who has literally been cornered.
She stuck to her guns and had to deal with the consequences.
...Did we watch the same scene?
Kara is calm for the entire trial. She doesn't scream. She doesn't throw insults. She doesn't fight the guards. She doesn't beg for her life. She doesn't even deny who she is.
She explains exactly why she feels the way she does.
She tells Arthur that people like her have been persecuted for years. She tells him she fights for freedom. She tells him she fights for the right to exist. She tells him she does not believe resisting an oppressive king is a crime.
Arthur doesn't actually engage with any of that.
His entire position is essentially, "Say you're sorry, admit you were wrong, and maybe I'll spare you."
But why would she apologise for resisting the very regime that has spent decades killing people like her? From Kara's perspective, she'd be admitting that her people's oppression was justified. She refuses because she genuinely believes she's done nothing morally wrong.
And then Arthur sentences her to death.
This is the part people always leave out: the episode does not present Arthur's decision as correct.
Merlin repeatedly argues for mercy.
Mordred begs Arthur to spare her.
Arthur ignores both of them.
Mordred loses the last person he loves because Arthur chooses execution over compassion.
That decision is literally the turning point that pushes Mordred away from Camelot and into Morgana's arms. Kara's death is one of Arthur's great tragic failures because it proves that, despite all his promises of building a better kingdom, he still cannot separate justice from vengeance when it comes to people associated with magic.
If the writers wanted us to think, "Well, she attempted murder, therefore Arthur obviously made the right choice," then the entire rest of Series 5 makes absolutely no sense. Her execution isn't framed as justice. It's framed as a catastrophic mistake that seals Arthur's fate.
So no, I don't agree with reducing Kara's story to "she tried to kill the king and faced the consequences."
She was a Druid who had lived under lifelong persecution. She was hunted down while injured and cornered by armed men. She defended herself when escape was impossible. She was captured, refused to renounce the beliefs she'd formed through a lifetime of oppression, and Arthur chose execution over mercy despite being urged not to.
That's what actually happened. Reducing all of that to "attempted murder" strips away literally everything the episode is trying to say.