It's hard to say for sure. Deku has grown a lot, but All For One is a powerful villain. It depends on various factors like their current abilities and the circumstances of the battle.
In 'All for One Deku' fanfiction, it's interesting to explore the new relationships Deku would form. For example, his interactions with villains who were once on the opposite side of him. Also, the power dynamics shift. Instead of being the underdog hero, he could potentially become a more complex and morally ambiguous character with All for One's powers. His internal struggle between his original self and the new, darker influence can create really engaging storylines.
One common theme is the power of mentorship. All Might being Deku's mentor, fanfictions often explore how that relationship affects Deku's growth. Another theme is the transfer of ideals. All Might's 'Plus Ultra' attitude is passed on to Deku in many stories.
One common theme is mentorship. All Might is Deku's mentor, so a lot of fanfics explore how he guides Deku, like teaching him how to use his power effectively.
If Deku had One For All early, it could either make him a hero sooner or cause him more problems. It might make his enemies step up their game or force him to face even greater threats. It's a fascinating what-if scenario that could go in many different directions.