@Castelmore:
"the full potential of his fruit".
Because every fruit has its potential.
Magellan's one is really deadly. It's a poison's role. Other fruits aren't that dreadful.
And once Magellan controls his DF like a pro, it makes things crazily easy for him, as he's a real tank. It's not the case of other chars with their DF.
Well honestly, the Poison fruit is just going to hard counter people who fight with point blank melee attacks, or have no ways of bypassing an armor of sorts. While the Poison fruit is good, it seems like it would be hard countered by any fruit like the Bomb fruit or Wax fruit. Essentially, the only people you saw that were even remotely powerful in Impel down had fruits that weren't very good at fighting Magellan.
It's a strong fruit, but the only person with an ability worth a damn that could fight it was Mr. 3, who is comparatively very weak to the three strong people who "fought" Magellan (Iva, Luffy, BB), all three are fighters that go head to head with an enemy with fruits that don't really change that or simply enhance that quality of rheir brawling style (well that has changed with BB post Magellan fight though). Essentially you saw a Poison man, with a very well developed power, fight people who are going to get beat by Poison without some sort of method of neutralizing it, so it looked far stronger in comparison than it may actually be.
Bellamy's fruit could have very well been used to have extremely strong bursts of speed. Luffy for example, needs to pump his blood in an odd way, while Bellamy, could easily rival the startup attack speed of Gear 2 with a developed fruit on the assumption that he used his fruit well without so much as damaging his body. Luffy's attacks use wind up and the momentum from that wind up to make his impact stronger. A spring can do something similar much faster. The fruit is also limited by Oda's creativity. The spring fruit could be used to brace impact caused by a physical blow to something like a wall and rebound with absolutely zero damage as just an example. Yes, he would still lose to a Poison man. But what happens when you pit a fully developed Mr. 5 against Magellan? He could easily just snipe away at Magellan and depending on how the poison works, could cause it to explode doing more damage to Magellan. A Quake man could likely do something similar, use shockwaves from far away to damage Magellan.
There's really no black and white in One Piece fruits, it's entirely up to the creativity of Oda, how developed the character is, what kind of fruit they have, etc. I hardly think characters are directly limited by their fruits, because you can be strong in many ways depending on your fruit, and after all, it's a story written by the author, as long as it's plausible (and the powers are so ridiculous at this point, many things -are-) then really, many things are possible and fruits could be used in ways you may not have thought of. Seriously, don't shoehorn power into a fruit, shoehorn power into the specific matchup, Oda's imagination, and the characters.