there's actually something extremely powerful to me about how....not powerful dragon is being portrayed as in this flashback.
he doesn't have a devil fruit yet, he hasn't used any haki, hell he hasn't fought back at all beyond tranquilizing a celestial dragon from behind. he knows he can't free all the slaves or stop the hunt or stand up to the holy knights. he can only save two babies, and even then, he is nearly killed in the process (only surviving by sheer luck rather than strength or skill) and ends up losing one of them.
the purpose of showing dragon here isn't to reveal how badass he is, it's to show that even as a seventeen year old low-ranking marine who gets nauseous at the sign of violence, he was ready and willing to question the system around him. and honestly, that's a more impressive feat to me than any show of physical strength.
speaking of which, we haven't seen many (well, actually, any) feats of physical strength from dragon yet in the story in general and tbh i think that's fully intentional. i think dragon is a character similar to robin, where he CAN fight, but only because he has to in order to protect himself and his cause. his real value lies in his intelligence, leadership and steadfast moral core. if he never had to fight another day in his life, he'd be more than happy.
by contrast, dragon's father is a man whose reputation revolves entirely around his physical strength. his nickname is "the fist". his whole thing is just punching people really, really hard. yet garp is the one who has remained subservient to a system he doesn't fully believe in for fifty years, while his son was party to one act of government violence as a teenager and immediately defected and thought that dying might be what he deserves for the sin of his (extremely temporary) involvement.
but dragon didn't die. he kept going, kept moving, kept saving people. first it was that little red-haired baby, then it was entire countries, and now he's starving out the monsters at the very top. it's not about how hard he can punch his enemies. it's about political consciousness. it's about caring for people with no personal connection to you. it's about identifying the true rot at the heart of the world and being unafraid to question it, even if it might get you killed.
that's what makes dragon one of the strongest characters in one piece.