Long before meeting All Might and inheriting One For All in My Hero Academia, Midoriya Izuku had resolved to become a hero. To make his dream a reality, he began studying the Quirks and attack patterns of better fighters and soon discovered he had a knack for battle analysis that no Quirk could replicate. One For All may have taken the spotlight from his impressive intellect but Midoriya's achievements throughout the Sports Festival -- and all of Season 2 really -- showed he may have enjoyed some success even as a Quirkless Pro Hero.
The secretive nature of the games meant no student knew the obstacles the Sports Festival would hold. Predictably, the beginning of the first event, a race, favored Midoriya's Quirk-bearing classmates who would be able to bypass the robots. Bakugo Katsuki and Todoroki Shoto used their versatile Quirks to evade the robots' attacks while Kirishima Eijiro and Tetsutetsu Tetsutetsu powered straight through their first challenge. Unfortunately for Midoriya, neither of these options were open to him.
At this point of MHA, Midoriya hadn't yet mastered control over One For All meaning he could only use the Quirk at its full capacity. A 100% strike meant sacrificing whichever body parts he manifested his power through -- a sacrifice he couldn't make so early in the festival. Nevertheless, Midoriya rose to the occasion spectacularly. Using an abandoned piece of robot armor as a weapon, he baited one of the robots into charging at him and used its own momentum to slice its arm clean off. This close-quarters battle wasn't as flashy as his classmates' Quirks, but it was a lot more impressive since it required him to calculate the exact moment he needed to strike under unimaginable pressure.
The next opportunity Midoriya got to shine was at the race's final stage -- the minefield. Realizing he was hopelessly behind the frontrunners and that a careful approach would leave him dead last, Midoriya gathered as many of the weak landmines as he could. Then, using his makeshift shield as a buffer, launched himself on top of his pile, creating an explosion that catapulted him to the front of the pack in an instant and ultimately winning the race. Without using the tiniest percent of One For All, Midoriya was competent enough to beat all of UA's first years in an obstacle race that clearly favored those with powerful Quirks.
Midoriya continued to exhibit his trademark "calm under fire" analysis throughout the MHA's Sports Festival. When he was singled out as the possessor of one million points in the cavalry battle, Midoriya kept his cool and managed to procure a respectable team despite the limited selection of students who were willing to throw their lot in with him. The team made up of Uraraka Ochaco, Hatsume Mei, Fumikage Tokoyami and Midoriya himself succeeded in hanging onto the ten million point band until the very end, when they were helpless to defend against Iida's Reciprio Burst.
In the semi-final match against Todoroki, Midoriya's analytical skills and information-gathering ability were put to the ultimate test. Unlike popular heroes, he had no prior information on Todoroki's attacks. Midoriya was forced to come up with an original plan even as Todoroki relentlessly pressed him with avalanches of ice. The only way he could negate Todoroki's attacks was by sacrificing his fingers and using One For All at 100%, which he did with no hesitation, and continued to formulate a counter-attack plan while under immense pain.
Midoriya’s eagle-eyed observation helped him realize Todoroki's repeated ice attacks were slowly weakening the young prodigy. Any other combatant might've exploited his hesitance to use his flames instead, but Midoriya admonished his opponent for not taking the competition as seriously as everyone else. His words of encouragement convinced Todoroki to unleash his flames and decided the match in his favor, but it was a far lengthier one than Shoto had ever fought on screen. One For All allowed Midoriya to counter his attacks and even get a few hits on his opponent, giving him a glimpse of victory. But without his intel gathering and acute understanding of Quirks from extensive study, all it would have done is prolong an inevitable defeat.
One For All certainly was Midoriya's biggest stepping stone toward becoming a hero but he isn't defined by just his power. His dreams of being a hero were nothing more than a pipe dream before meeting All Might, yet that never deterred him from preparing for that future.
Time and again in My Hero Academia, Midoriya has shown how much of a boon his notes on heroes are. After studying Quirks for years, he's able to adapt to the new One For All abilities without much trouble and even gives his classmates some pointers on how to use their own Quirks. Midoriya's greatest asset has always been his mind. One For All makes his body strong enough to keep up with his plans but Deku's intellect, bravery and resolve have always been his own.