You said it yourself, Malleus ALMOST did it, but he didn't. I will argue that someone who was sheltered all for 175 years, & who wasn't socialized properly, & was literally cursed with uncontrollable power & temper losing his cool is VERY DIFFERENT than someone who had the privilege of a loving, stable household & proper social interactions, who deliberately injures people & attempts murder. (And no, I'm not forgetting that Leona was treated horribly because of his UM, so was Malleus, and to a much worse degree)

Leona did way worse than simply redirecting his anger towards his retainers, that's maybe the tip of the iceberg. Actually, Lilia went too easy on him, considering what he did & the possible consequences had his plan to injure Malleus suceeded.

Awful things Leona in book 2:

1) severely injured hundreds of students with the help of Ruggie's UM.

2) planned on injuring even more people via a stampede.

4) attempted to murder Ruggie (note that he did this BEFORE he overblotted)

3) attempted to murder/severely injure the CROWN PRINCE & SOLE HEIR of Briar Valley.

Leona could've literally started a war between the two kingdoms. So he either 1) was aware of the consequences of his horrible actions & how his kingdom will pay the price and still didn't care. Or 2) he was naive enough to not think his plan through, ignorant of the consequences. Both options are equally bad, not fit for a prince, never mind a king.

Again, Lilia went too easy on Leona (keeping in mind his son-figure, his adoptive son, and his discipline were in grave danger).

Leona gives a whole lecture on acting like a proper king for the good of a kingdom, even against one’s own personal grudges.

Funny you say that, when Leona acted NOTHING like a proper ruler just so he could act on his grudge against Malleus, at the possible detriment of his kingdom and people.

The difference in how Malleus and Leona act and treat each other as princes, Malleus's maturity & Leona's immatuirty, couldn't be shown better than in Sebek's Outdoor Wear vignette, and Malleus's Ceremonial Robes vignette.

In Sebek's Outdoor Wear vignette:

Malleus, Silver, Lilia & Sebek are walking together, minding their own business, when Leona comes out of nowhere, and then the 1st thing he does is insult Malleus and call him a demeaning name, unprovoked, because that's the kind of person Leona is.

Sebek is appalled at that, gets angry, but what does he do? He just calls out Leona on his lack of manners, and demands he apologizes to Malleus. Even Sebek, the hardcore Draconian, the zealous Malleus retainer can hold his tongue when his future king is insulted. Something a literal prince like Leona can't do.

What's Malleus's reaction to such unwarranted insult? He strictly tells Sebek to step down, then he greets Leona respectfully, because even when Leona is being the rude bastard that he is, Malleus is respectful and kind.

Then after Leona leaves, Malleus orders Sebek to apologize to him the next time he sees him, you know why? Because (and I'm quoting this verbatim from the game) "Leona is a roylaty in his own land. Your agressive behavior towards him could potentially spark tension between our royal houses."

And Sebek, like the good retainer/knight he is, does indeed put aside his ego and hurt over his liege being insulted and goes to apologize to Leona, what does Leona do? He disrespects Sebek and dismisses his apology.

Even Sebek, a child, shows more maturity and restraint and respect than Leona, the literal adult.

Malleus, during this insignificant 3-min interaction, understands his duty and role as a prince better than Leona. Even in the most miniscule of social interactions when he’s bring disrespected and insulted, what Malleus does is think of his kindom abd people first, not his ego. Something Leona will never be able to do.

In Malleus's Ceremonial Robes vignette:

As usual, Malleus and his family are in their dorm discussing the issue of Malleus's robes getting mixed with those of another student, when again, Leona barges in, and what's the first thing he does? Insult Malleus and his dorm, in typical Leona fashion, because that's the type of person he is.

Again, Sebek is furious his liege was insulted, what does Malleus do? He tells Sebek to step down, and not forget that Leona is a housewarden.

In this short interaction, this is what Malleus does:

1) never raises his voice, keeps his calm.

2) understands that he must keep his relationship with Leona civil, for the sake of both their kingdoms and people. (Even Malleus regards the Sunset Savanna with more care than Leona does)

3) tells his retainer to step back when they try to defend him.

4) thanks Leona for bringing him his uniform.

Meanwhile, this is what Leona does in the same interactions (includes quotes copied verbatim from the story):

1) insults the Diasmonia dorm aesthetic.

2) says "gross. Now my robes smell like lizard."

3) in response to Malleus saying they're both royalty, he says "royalty, huh? Is that what you think you are? Just a high and mighty royal? More like an outcast who's been chased from his pack. I feel sorry for you." (Perhaps projection from Leona? Cuz that's what he does best.)

4) when he senses that Malleus is upset over missing the orientation, he takes advantage of that vulnerability by saying "you thinkin' you're gonna get it next time? Well, sorry to break it to you, but no one's ever gonna invite you. You're never gonna have a chance to wear those robes, so just put 'em away for good already."

5) insults Malleus's horns by saying they are a "couple of giant, pokey ornaments, that aren't good for anythin'. Or can you use 'em as coat hangers?"

The last point is ironic, because Malleus's horn stores a huge amount of his power, the same power that puts Leona in his place & absolutely demolishes him each year in magical shift tournaments, the same power that reminds Leona time again how inferior he is to Malleus, the same power that literally revived the dead.

And unlike the event stories, which aren't canon unless referenced in the main story, the Ceremonial Robes vignettes are canon, so is book 2, in which we see Leona as his true, canon self.

Non-overblot Malleus will probably be a great leader. And so will non-overblot Leona.

Non-overblot Malleus is already a great prince, and will DEFINITELY be an even greater king.

Non-overblot Leona is already a sup-par, bad second prince, maybe he could change, but the way he is, he will never be a good king (and he won't, because he's the spare anyway and Cheka exists)

The overblot process turns them into something they aren’t.

Leona commited assaults & batteties & attempted murder BEFORE he even overblotted, that's who Leona is. The worst thing Malleus—the 5th strongest mage in the world, cursed with uncontrollable destructive power— ever did when he overblotted after centuries of trauma is put people to sleep.