We see that as a villain, Midoriya would be terrifying. That fact that he is very good at analysis and figuring out the best way to use the information works for him very well. There's a reason why the blurb states he's showing people they should be glad he didn't go the villain route.
It is all too easy to imagine this as a real-life event rather than a school exercise at some points. A hero team led by an abrasive self-important icon is confronted by a villain who knows their leader inside and out. This villain has no problem leaving a trail of bodies and broken buildings in his wake, and his blitzkrieg of crime runs an ever-dwindling team of heroes ragged through failure after failure as superior planning, equipment, training, and teamwork propel his criminal empire to total domination.
The first scene at the bank, described as chaos with broken or faintly struggling civilian bot bodies. It's too easy to imagine the robotic civilians replaced with dead or dying people.
Midoriya blows up a bank. Cheerfully.
Tsuyu's "death" in the sewers. After Tsuyu becomes separated from her group, she encounters Kuroiro, who promptly uses his Quirk to erase all the light around him and sends forward the shadows in the shape of grasping hands. The sight of it gives her flashbacks to when where Tomura nearly grabbed her, causing her to blunder into a paint bomb as she flees in panic. Her teammates only find out she's gone when they happen across the note she scrawled in the paint, which looks eerily like blood.
Earlier in the sewers, Tokoyami keeps the Heroes on edge by continually sending Dark Shadow back and forth, all while it laughs maniacally. It's one of the moments where you wonder whether the Villains are playing their part well, or they are enjoying it too much.
In one of his actions, Shoji quickly takes out a dozen "security guards" with his multiple hands by either crushing their skulls or just ripping their heads off. Remember that the big guy has canonically the strength to do so.
Monoma copies Setsuna's Quirk and rips off his broken arms to regrow them. And before that, he had chopped off the tip of his pinky finger. The former moment causes Present Mic, who is monitoring the exercise along with the other teachers, to throw up.
Extortion uses her Quirk to garrote a robot and then she, Lift (Yanagi), and Drug Runner (Mina) melt the body and Extortion's hands in acid. Extortion is visibly disturbed by the whole ordeal, like she killed a human being.
The villain team drugs Momo, Awase, and Fukidashi and has Con Man brainwash them into building them an underground bunker before executing the three as an event within a party. A fourth victim is a robot that was convinced to give up his part of a special code before being callously "killed".
Powerhouse attacks Kingpin in a storage room and just when things seem to calm down, and they start talking things out, Powerhouse flips out (he thinks Kingpin is making him talk about his past bullying while the teachers are monitoring them, so to have him expelled) and attacks even more ferociously than before, trying to maim Kingpin seriously. Even worse, the storage room contains crates filled with vials of Powerhouse's sweat. Even Kingpin shooting him with one of the paint guns (and thus eliminating Powerhouse from the game) doesn't stop him, and it takes Ectoplasm knocking Powerhouse out and physically removing him from the area to stop him. The author said right that moment Kingpin is so terrified he's basically regressing to the times he was bullied in middle school.
During the Final Battle, the villains go as far as using methods that put some of their own in danger, prioritizing the results over the well-being of their comrades. They crash an helicopter (a model made life-size with Kodai's quirk) next to the cells where some of them are imprisoned to free them, and shortly later Temperance covers a downed Kendou with fake blood only to provoke and distract Tokoyami and let Prism narcotize him, just in time before a furious Dark Shadow attacks Animal. It would have taken little for some people to be seriously injured.
In general, the Villains side of the exercise increasingly slipping into a truly villainous mindset. Their attacks and methods get increasingly brutal and twisted, and they are often even gleeful about them. They are definitely winning, eliminating almost half the heroes over the first 24 hours, yet they are rabidly furious for a few losses on their side. A few, like Extortion and Crudade, seem to still realize they are going too far but for most of them, it feels like watching one of those social experiments going very bad. Even their Nezu expresses worry that the villain mindset is becoming so ingrained in them it may ultimately become their undoing, because they're forgetting to think like heroes and therefore understand their opponents. Even if they ultimately win, it's clear it's taken a toll on all of them that will take at least some time to heal.