Welcome to the Anime Walk of Fame, a series of retrospectives on the many characters of the anime world. You'll see all your favorites along with a few that deserve more than their reputations give.

So sit back relax and enjoy the show.

Buggy Knows the System

There's a good reason why I saved Buggy until last.

Buggy is the first devil fruit user faced by Luffy, but became the butt of jokes after being defeated but kept alive for the majority of the series where he seems to indirectly influence major events following the breakout of Impel Down, effectively his position of power was achieved not through power but by clout as he knows Shanks personally and is at least acquainted with a number of major players, this allowed him to ascend to the Emperor's position with his Cross Guild group where he places bounties on marines, the fact that Crocodile and Mihawk join him for this, really helps, although both former Warlords wouldn't hesitate to use him as the scapegoat if things go wrong, this also calls the bounty system into play as it's less power level measuring and more level of clout and overall danger level in the world.
Also worth noting is that Buggy is one of the hardest pirates to kill with him able to split into pieces, it would become seriously OP if awakened.
Buggy essentially achieved his position through clout alone despite being a mid boss at best, some seem to think he would even grab the One Piece only to lose it to Luffy as part of the ending.

Arlong Makes No Sense

Back in East Blue, nothing was more intimidating than the fishman Arlong but in the grander scale of One Piece, Chopper could probably defeat him.

So he takes over a village to make it his base of operations and bleeds the people dry of their money and forces Nami into making maps and charts for one day rising up and taking over all the while paying off corrupt marines to not arrest him, this is where his plans start showing cracks; in the bigger picture, Fishmen are meant to represent the oppressed society, so when you do eventually learn about other fishmen and their struggles you become more sympathetic, all the while accepting that there are just flat out racists among said oppressed society such as Hody Jones, but you don't learn that until after the time skip, so when live action Arlong spells it out to you, the impact is kinda lost.
To play Devil's advocate if I did know about the fishmen's past going into Arlong Park, I would've thought someone of Arlong's strength could be a much bigger threat, instead he's a common pirate who couldn't hack it on his own and needs humans to do things that he should have no problem doing in the first place.

Don Krieg is Useless in One Piece

Alas poor Don Krieg, he never stood a chance.

Don Krieg was intended to show that even the most well prepared pirate is no match for the Grand Line as he gets defeated by Mihawk just for disturbing his sleep, in fact I don't think he even made the Grand Line.
Sad because his arsenal would make him a legitimate threat in any other anime, but here, he's about as worthless as Tenten from Naruto.
Exploding spears, a strong shield, stake launcher, poison gas launcher, capture net launcher, spiked cape, multiple guns and a fleet of ships under his command but still lost to a grumpy swordsman.
Any wonder his role is reduced to fodder in the Live Action Netflix adaption.

Kuro is Pretty Dumb

It seems odd for me to refer to Captain Kuro as dumb when he's easily one of the most intelligent characters in the show but his decision making had more holes than Swiss Cheese.

To be fair, I doubt he'd planned for Luffy to show up, in order to evade capture, he used Jango to hypnotise Axe Hand Morgan, the only survivor of Kuro's massacre into thinking Morgan captured him but placed a fake instead, pretended to be a victim of pirates to gain trust into Kaya's estate as her butler, the fact that he already looked and sounded the part helped, he also gambled on the town eventually ignoring Usopp's cry wolf phase and even stopped a mutiny when he was called out by his crew for how long the plan was taking, but he made the fatal mistake of being too impatient when attacking Merry, when if he managed to just not react to Luffy and his crew, he may have actually succeeded, the sad thing is that he is the most intimidating villain of the original six starter villains, since then he's floating about the seas, as a free man anyway since in the eyes of the world, he's dead but any attempt to comeback in a world of ever stronger pirates and his reasons for wanting out in the first place is being that the world was too chaotic to tirelessly keep going, I think it's safe to say that Kuro wants nothing to do with the One Piece world anymore.

Morgan Isn't The Best Introduction To The Marines

Now for the second lowest impact villain in the show.

Axe Hand Morgan was the first Marine villain encountered by Luffy, we see that Morgan is completely full of his own self importance when he claims to have caught Captain Kuro of the Black Cat pirates not knowing he has been hypnotized.
This translates in him essentially ruling with a literal iron fist, exemplified by how spoiled his son Helmeppo acts in the beginning, after his defeat, he gets a Court Marshall from Garp but taking advantage of Garp's lax approach, he escapes by threatening to kill his own son and has been on the run since.
With Marines meant to be the antagonists rather than out right villains, starting with Axe Hand Morgan isn't exactly the best choice for this, Smoker on the other hand is a much better choice to fulfil this role and does so well, despite his even scarier appearance he's shown to genuinely care about the public making him a perfect representation of the marines rather than Morgan.