It seems sense that the main character in the My Hero Academia manga would get stronger as Deku continues to gain One For All's several potent Quirks. Deku demonstrated Gear Shift in Chapter 369, the young hero's sixth and final Quirk.
Gear Shift's transformation into a genuinely scary power during the years it spent imprisoned inside One For All also happens to make up for one of Deku's biggest vulnerabilities in the anime.
What is the weakness of Deku that needs to be overcome in My Hero Academia
Gear Shift originally belonged to the still-unnamed second user of One For All and allowed him to alter the trajectory and motion of objects -- as long as they were no larger than a bullet. By his own admission, it wasn’t a particularly impressive Quirk. In Deku’s hands, however, it’s blossomed into a power that allows him to ignore all the traditional laws of physics and motion. When Deku activates Gear Shift on himself, he has total control over his body’s movements.
Before Deku began unlocking the previous users’ Quirks in My Hero Academia, he could only rely on One For All’s base power-stocking ability. He developed Full Cowling and Shoot Style to better manage the Quirk’s overwhelming power, but these were merely imperfect stop gaps he had to rely on until he fully mastered One For All. As helpful as they were, those super-moves were not without their weaknesses.
Even as a hero in training, Deku couldn’t figure out his limits in carefully-controlled scenarios. The greatest test of his Shoot Style and Full Cowling moves in the MHA anime has been his battle against Overhaul in the "Shie Hassaikai" arc, and the yakuza boss identified his weakness after a very short exchange of blows. Overhaul observed that Deku had quite impressive speed and power back then with One For All at 20% -- but his attacks were always launched in a straight line. This habit of Deku’s meant his attacks would always be predictable -- and therefore exploitable -- to observant enemies.
How did Gear Shift overcome that weakness for Deku
Even for someone as dedicated to constant improvement like Deku, this was a nearly impossible weakness to overcome. Since One For All was a gifted Quirk, the speed and power he used to terrorize opponents was just as new to him. While in motion, it was impossible for Deku to alter his course due to the high speed at which he traveled. Fortunately his new Quirk, Gear Shift, allows him to bypass this weakness entirely.
When Deku finally confronted All For One at UA, their exchange harkened back to his battle with Overhaul. Even though he was several times faster and stronger, his attacks still followed the straight-line pattern Shoot Style had ingrained in him. Never one to miss anything, All For One immediately began preparing to intercept Deku once he figured out the young hero’s attack pattern, but discovered to his dismay that Deku had already outwitted him.
The blow he’d readied for Deku completely missed its mark -- not because All For One’s mental calculations were inaccurate, but because Deku had instantly switched from impossibly high speeds to a dead standstill. Under normal circumstances, the momentum he gathered should’ve sent him flying straight into All For One’s waiting attack anyway, but Gear Shift allows him to completely ignore the laws of inertia. With his new Quirk, Deku will remain in complete control of his body’s movements even when pushing One For All’s power to the extreme. That’s one less weakness for My Hero Academia's villains to exploit.