Leon was already known to be strong all on his own, but imagine how stronger he'd be if he had a great figure that was with him throughout his continuous years of being champion (no, not rose.)
He always had this little fear of "that's his limit" and that "he can't get any stronger than that" that he grew up with and sadly got proven when he was unbeatable, so imagine if he had a great figure who he can trust his worries with when he was young
Someone that can answer his "Can I get even better?" With "Everyone keeps improving" or "Believe it or not, there will always be someone better than us. That's why we always have room for improvement." So imagine how much stronger he would've been as he grew up, knowing that he can keep going further no matter what