In One Piece, the Straw Hats' Nico Robin is considered to be one of the most dangerous individuals in the world. With the ability to read the ancient Poneglyphs, an ability lost to time long ago, Robin is capable of finding and potentially commanding the Ancient Weapons -- as well as uncovering the truth behind the Void Century.
Considering how much of a threat that would be to the World Government, they promptly decided to put a 79,000,000 berry bounty on her head at the age of eight. While her bounty has increased even further since then, it has mainly been due to her association with the Straw Hat Pirates, but in reality her potential is much more dangerous than they realize.
Nico Robin uses the Hana Hana no Mi, which lets her sprout up to 1,000 limbs (or other body parts of her choice) at will. She can summon them on her own body or on any surface aside from seastone, as well as have them merge together to create giant limbs capable of taking out whole swarms of enemies. Her merging ability can also take the form of wings, nets and other non-limb constructs. This power-set has made Robin a formidable foe for many in One Piece, and is the key reason she managed to survive in a world trying to hunt her down -- but even so, she has yet to utilize it to the fullest extent.
As useful and versatile as Robin's ability may seem, it has one glaring weakness. If any of her sprouted body parts are injured in any way, the damage is reflected back to herself. This makes her power somewhat double-edged -- every limb she sprouts acts as both a means of attack and a target for enemies to take advantage of. That being said, there is an obvious counter that could potentially eliminate this weakness altogether.
As of late, Haki has become one of the most important aspects in One Piece, with most major characters having it and able to utilize it quite well. Armament Haki in particular has been seen the most and coincidentally would make Robin a true force to be reckoned with, even against more advanced users.
By coating limbs or weapons in Armament Haki, characters are able to enhance the strength of their attacks exponentially while also increasing the durability of whatever is coated, making them virtually unbreakable. If Robin were to coat her sprouted limbs in Armament Haki, she would become practically unstoppable, as her opponents wouldn't be able to hurt her through attacking her sprouted parts.
Observation Haki would benefit Nico Robin quite a bit as well. By being able to sense and detect things on a higher level, she could use her Haki to determine the best place to sprout limbs and parts in order to best her opponents. This would be similar to how Spider-Man unconsciously uses his spider-sense to determine where to shoot his web line when he is web-swinging.
Since the start of One Piece's Wano arc, her powers have seemingly grown much stronger, yet they're still not necessarily where they could be. Robin is able to make fully autonomous clones of herself that are capable of gathering information as well as fighting, as seen when she was escaping from Orochi's ninja. She has even learned how to incorporate Fishman Karate into her attacks, giving her more options against enemies than her usual grappling techniques did.
More recently during the raid of Onigashima, Robin displayed an ability called Gigante Fleur that creates a giant copy of herself that fought Black Maria head-on without assistance. Perhaps her most devastating new ability is the Demonio Fleur, which is much like her Gigante Fleur -- except her sprouted copy looks demonic with extra limbs to add to the horrifying image.
Robin has definitely become stronger since she joined the Straw Hat Pirates -- especially with her devil fruit -- but she could still be so much more. If she were to learn Haki, master Fishman Karate or another kind of martial art like the Six Powers, Robin could easily become one of her crew's powerhouses.
While it should be noted that she is considered one of the main combatants on the crew, she's always chosen to learn just enough to help her get by or be useful to her friends. She uses her abilities to support her crew more so than she does to fight for them, though she's more than willing to do the latter too.
After her hard-earned victory against Black Maria in One Piece, it's possible that Robin will want to get stronger to make her fights easier to win, especially considering she was fighting to save Sanji. All in all, could Robin become stronger? Yes. Will she? Almost definitely. But will she become the strongest member of the crew? Unfortunately they aren't called the Robin Pirates, so probably not -- but that doesn't change the fact that her potential is massive.