The Justice League is DC's greatest assemblage of heroes, battling against the deadliest threats in comics. The League is the team that every hero wants to join, and its members have run the gamut from powerless vigilantes to all-powerful aliens. They've needed every kind of hero in their battles, but it's impossible to deny that their most powerful members are the most obviously useful.
Superhero comics are known for bending credulity simply by introducing superpowers, but many Leaguer's abilities obviously break readers' suspension of disbelief with powers that make no sense. They're entertaining and they've made a huge difference, but that doesn't change their nonsensical nature.
10 Hawkman
Hawkman has a long DC history, first appearing in the Golden Age. A founding member of the Justice Society, Hawkman would eventually be brought into Silver Age DC. There are several versions of the character, but one thing that stayed the same throughout his history were his Nth metal-endowed powers: flight, enhanced strength, and a healing factor.
The flight makes sense since Nth metal is usually considered an antigravity metal. This even makes his enhanced strength make sense in its way since it can nullify an object's mass, if not its inertia. His healing factor doesn't fit in. Fictional antigravity metal should do a lot of things but healing people isn't on the list.
9 Zatanna
Zatanna's magic mastery has made her a clutch member of the League time and again. Trained by her father Michael Zatara, a Golden Age magical hero, she eventually mastered a very particular type of spellcraft. Zatanna focuses her spells by talking backward. This has always made for a unique way of doing magic in a comic, but that doesn't mean it makes sense.
Most magic rules in comics, sci-fi, or fantasy work because the user knows particular spells. Zatanna's power breaks every established magical rule, and rules are very important to magic. Zatanna's powers are cool, but they make no sense in any established magical system.
8 The Atom
The Atom has always been among DC's premiere scientific heroes. Ray Palmer created a size-changing belt using a white dwarf star fragment, allowing him to shrink to subatomic sizes and completely control his mass. The Atom was the League's best infiltrator, as well as one of the team's "big brains," helping them with their biggest scientific problems.
The Atom's powers completely break the rules of physics in every way. For example, the density of the dwarf star fragment would make it impossible to lift, let alone turn it into an accessory. Ray changing his mass also makes no sense, since shrinking doesn't change the number of molecules he's composed of. The Atom gets by because there's a semblance of science surrounding him, but it's not good science.
7 Plastic Man
DC has some weird B-list heroes, and Plastic Man is among the weirdest. Plastic Man has a long history in comics, first appearing in 1941. He's the ultimate stretchy hero, and also the most powerful. Not only can he stretch, but he can also shapeshift. He has complete control over his body. Even Batman respects Plastic Man, despite his buffoonish tendencies, and fears his potential.
Plastic Man's shapeshifting isn't that weird for someone with complete control over his body. However, he can actually make himself into a working rocket or airplane. His shapeshifting goes way too far for a man who can alter his form but shouldn't be able to completely change his chemical composition, like Metamorpho.
6 Shazam
Shazam was one of Superman's first imitators, but he's always felt like a unique personality. Shazam's powers are magical and make him one of DC's strongest heroes. The Wizard Shazam gifted him with the wisdom of Solomon, the strength of Hercules, the stamina of Atlas, the power of Zeus, the courage of Achilles, and the speed of Mercury.
The strangest aspect of Shazam's powers is the way they come from such disparate sources, from Biblical figures like Solomon, Greek heroes like Achilles, multiple gods and titans, and a demigod. All of their powers make sense on their own, but mixing them all together always felt strange.
5 The Flash
DC has created the most powerful speedsters and the Flash is their king. There have been multiple Flashes, and both Barry Allen and Wally West have been Justice League members. The Flash has always been among the most powerful Leaguers, but his speed powers have always been a bit fantastical.
For example, vibrating his molecules to phase through objects never made sense. A lot of other factors - like his metabolism, friction, and other practical concerns surrounding super speed - used to not make any sense, but the Speed Force helped writers handwave these issues. However, the Speed Force itself also has some nonsensical angles, like the fact that it's an energy dimension that's somehow anchored in Barry Allen. Every level of analysis creates new issues for the Flash.
4 Green Lantern
The Green Lantern symbol is among DC's most recognized symbols. Several Green Lanterns have been a part of the Justice League, including Hal Jordan, John Stewart, Guy Gardner, Kyle Rayner, Jessica Cruz, and Simon Baz. Their power rings made them clutch members of the League. The Green Lantern Corps' rings are considered the greatest weapons in the universe, but there are some problems.
Green Lanterns' rings' limits have never been well-established. It's said they can do anything the bearer can imagine and has the willpower for, but that's been proven false, particularly when Hal Jordan tried to remake Coast City. The boundaries surrounding their constructs have always been a grey area and the rules change whenever the stories need them to.
3 Firestorm
Firestorm is a combination of college student Ronnie Raymond and professor Martin Stein. The Firestorm matrix was created by the government to make a superhero, and it gave the new composite being great power. Firestorm is a cauldron of nuclear energy and also has super strength, invulnerability, flight, phasing, and molecular control
Several aspects of Firestorm's powers don't go together, however. The super strength, for example, feels like an anomaly. His ability to phase sort of makes sense with his molecular control powers, but those powers are more like putting elements together to make compounds, so simply walking through walls is a stretch. His nuclear powers also always felt like an unneeded addition. Firestorm is a little bit of everything and that never really makes sense.
2 Superman
Superman is a powerhouse like no other. It's debatable whether he's the most powerful member of the League, but he's done so much for the team it hardly matters. There have been plenty of times over the years that the Justice League never would have survived if it wasn't for Superman. He has an amazing array of powers, all of which come from the way Kryptonians metabolize yellow sunlight.
Superman's solar powers have never made sense. There's really no reason for someone who grew up under a red sun to have cells that would even know what to do with yellow sunlight. At best, it's a cosmic coincidence that he gains powers from alien stars and it's best not to think too much about it.
1 Martian Manhunter
Martian Manhunter never gets enough credit for how distinguished he is. The perennial Justice Leaguer is also among the team's most powerful members, with Superman-level strength, flight, shapeshifting, telepathy, Martian vision, invisibility, and intangibility. That's a potent laundry list of powers, and they make him a perfect powerhouse for the League.
Some of Martian Manhunter's powers can be explained by his alien, shapeshifting nature. However, his intangibility doesn't really go well with his other powers. Intangibility is always a strange power, and it's often paired with powers like super strength that don't make sense in context. J'onn's Martian vision is another weird one since laser-eyes aren't telepathic or shapeshifting and just make him feel more like an imitation of Superman.