Didact, I don't really feel like that's a fair assessment. Abe's actions weren't Leeroy Jenkinsy in the traditional sense-he was operating alone, but he didn't rush headfirst into combat in order to intentionally screw things up for other characters. Perhaps you didn't mean it in that regard, but Leeroy Jenkins implies he was intentionally trying to tank the RP for the other characters, which I don't feel he was-to me, he was simply approaching a typically-delicately-handled scenario with brute force, which honestly seems more in line with the creativity you said he should've functioned with. In fact, if I'm reading it correctly, there's no way the villains should've been able to tell that it was he who caused the attack, as it would've looked like the second floor simply collapsed. Saying that stupid behavior gets punished in the field of combat isn't really accurate either, given that (and I'm not calling anyone out, I'm just saying) we've had Agnes run off on her own to throw hand grenades at an army of zombies, Hot Rod charge headfirst into the fray, my own character run off on her own, and your own Zenith spearheading the assault, and nothing bad has happened to them, despite the fact they're up against a small army, comprised of hardened criminals and superpowered villains. The army would've been expecting an attack from superheroes as well; the restaurant crew likely never anticipated the floor falling through, and even professionals can be caught off-guard. Surely someone in the chaos would've made a break for the wide-open doors, which would've drawn the attention of the villains, rather than knowing it was Abe-unless their powers enable them to sense the usage of powers, which, while acceptable as a plot twist (it wouldn't be fun to know what our opposition's capable of), I still think Abe should've been given a fighting chance to at least flee the scene, rather than be abducted and put out of the fight indefinitely. Unless the phaser woman's power entails knocking people out with a single kick, there's also no way she could've incapacitated Abe so easily-he's an experienced street fighter and able to turn his body to stone at a moment's notice. It seems more likely she would've broken her foot against his head rather than her foot knock him unconscious.
Remarkable disregard for collateral damage I also don't see a problem with. Having VTOL's firing miniguns at a prison? I feel like there'd be a bit of collateral damage involved with that-not in the same sense of Abe collapsing a building, sure, but I feel like a small fleet of airships, a bunch of superheroes and supervillains duking it out, and the most powerful man on Earth trying to contain the situation causes some collateral damage. A lightning bolt strikes the prison walls? Sends bricks flying for miles. So on and so forth.
Having (and again, not trying to call anyone out) Agnes and Cordelia as members of the League seems to imply collateral damage is acceptable. I fail to see why the collateral damage was an issue-there's no rule against killing innocents or having to behave like an orthodox, straight-laced hero. If he'd caused an earthquake and killed everyone within the building, he'd have taken out a few innocent lives, probably killed himself in the debris, but still gotten the job done. Not saying that's morally right-and you've made obvious your disdain for antiheroes-but I still don't feel like it's fair to curtail his options while simultaneously telling him to be creative. Calling out Leonerdo for causing too much collateral damage is unfair-within the context of the RP, if he were kicked out of the League for what he did (or at least investigated), that would be understandable, but to be brutally honest it feels like Leonerdo found a way around the hostage situation and, given that it didn't fit with your plan for how that scene played out, his character was knocked out of the equation. It admittedly makes me question my own character's future in this RP. If you want this to be a very story driven RP, that's okay, and I'm happy to operate that way, but we were told in the OP that player choice was going to play a considerable role in the formation of the plot and that's been brought into question with how Abe was dealt with, along with how quickly the bomb threat earlier was brushed over.
Saying "you couldn't have expected to take them all out anyways" is somewhat alarming, as that would mean he was supposed to have been metagaming in order to RP properly. Given that Abe was in the restaurant, Abe's personality is one of arrogance and cockiness, and he's an experienced combatant, it is entirely in character for him to act the way he did. If you wanted this to be strictly a go-in-and-get-hostages scenario, I feel like it would've been fair to ask Leonerdo to post again, being outside the restaurant rather than on the inside, instead of putting him out of the game in the matter he was. I think we're fine with some constraints on the RP, that's totally understandable, but this one in particular is a bit of a blindside, especially given similar "Leeroy Jenkins" activities (pulling out a detonator in a room full of supers, charging headlong into battle, etc) have been allowed to carry out naturally whereas this was shut down somewhat abruptly. Futhermore, telling him he couldn't have expected to take them all out anyways implies he had no chance at all, which is honestly making me question the future of this RP. Will my characters be shut down, regardless of creative plans and tactics, if deemed necessary for the story? If so, I'd like to now right now, as to me it seems like a competent fighter with copious amounts of strength-with a hell of a sneak attack-stands a fair chance. While I can't comment on the powers of the two unknowns, it seems he could've easily destroyed the acrobat, taken the teleporter with a little work, and probably eventually worn down the phaser, or at least forced the phaser to retreat (thus saving the hostages). He may have been outnumbered, but he certainly wasn't outgunned. However, I think the main complaint Leonerdo has is that we can discuss the hypotheticals of this situation all we want, but he didn't get a chance to carry it out.
I have to share his concern, as I'm willing to indulge in a bit of our actions being curtailed and shaped towards a certain conclusion for the sake of a plot, but as long as it's in-character and believable, I feel like we should be able to witness the repercussions of those actions, and Leonerdo wasn't really given that chance.