My Hero Academia's Quirks have really changed the game. They're superpowers, but always with an obvious drawback. Deku destroys his body using his, Bakugo needs to sweat for his to work, and Todoroki can give himself hyper/hypothermia. These powers are weird a lot of the time, can be trained like a muscle would be, and usually need specific situations in order to thrive. So, let's take a look at the power systems in modern Shonen that managed to beat out MHA's Quirks in terms of design as well as critiquing the ones that don't.
10 Better Than: Hunter X Hunter's Nen System
Ask any big Shonen fan about what Power System has the most thought put into it, and at some point in the conversation, Nen will come up. Hunter X Hunter's Nen system is fun, has concrete rules and mechanics from the get-go, and has an upper limit for most people. It's a system to allows for weirdo powers like making your energy elastic-like Gum or using energy to stitch things together, but also must follow simple rules that anyone can learn.
9 Worse Than: Dragonball Z's Ki/Power Level System
Power Levels aren't the only way of measuring a person's power in Toriyama's Dragonball franchise. There's also Ki, a concept that is rarely used and mostly flew out the window after Goku graduated from the Kaioken to Super Saiyan. Ki is another take on the idea of "life energy" and is what actually makes up the number a person's Power Level represents. In the show, the laser beams, the aura around characters, and most of the techniques use Ki. It serves the purpose of the story, but it's about as shallow as you can get.
8 Better Than: One Piece's Devil Fruits
The Devil Fruits in One Piece are simple, they give you a superpower, but in exchange, you literally sink in water and can't swim. And, in the world of One Piece, most of the entire surface of the planet is covered in ocean.
Then, Devil Fruit abilities are separated into three categories called Zoan, Paramecia, and Logia. We don't have time to go into each one individually, but just know that this Power System is simple, open enough for the author to be endlessly creative, and restricting enough to stay consistent (most of the time). Like Quirks, the Devil Fruits are powers that come with unique drawbacks, and that usually is the sign of a well-thought-out power system.
7 Worse Than: One Piece's Haki
Speaking of One Piece, let's get into the secondary Power System they introduce after the 2-year Timeskip. Haki is yet again, another representation of using one's "Life Force" as power. There are three types, Observation Haki, Armament Haki, and Conquerors Haki. Each one does something different such as letting the user observe what the opponent will do next, guarding their own body or items, and imposing their will upon others until they pass out. Haki is pretty well thought out and the stronger users can beat everyone else's Haki. The only problem is, it exists to restrict the Power Ceiling of Devil Fruits, which is no fun.
6 Better Than: Avatar The Last Airbender's Bending System
Forget about if AtLA is considered an anime or not. Even if it isn't, it would absolutely fit into the categorization of a "Shonen" piece of media. So let's just move right past that and instead talk about how awesome the idea of bending is. Instead of controlling an element with the flick of a finger, benders in Avatar have to use special martial-arts influenced stances to "bend" the element to their will.
The concept has a ton of backstory and justification in the lore of the show, and each "element" of bending has unique paths of progression and visual flairs. It may not have much that "restricts" it like a certain amount someone can use in a day, but it absolutely is unique enough to make it one of the most memorable Power Systems in recent memory.
5 Worse Than: Fairy Tail/Black Clover's Grimoires
Let's be fair, the Grimoires in Black Clover are at least a half step above the ones in Fairy Tail. But, both of these shows are Shonen series where literal Magic is the fuel source warriors use to fight each other. And, magic is magic, it doesn't have to follow logic, and it doesn't have to necessarily run out. By that logic, characters can do anything the writer wants as long as they "believe" in themselves or their goal enough. And, that doesn't make for a believable or interesting Power System. Black Clover does it a tad better, but as a whole, Magic kind of takes the "resource management" part out of Shonen Battles, and that's more crucial than most people realize.
4 Better Than: Fullmetal Alchemist's Alchemy Skill
Equivalent Exchange. For every action, there is an equal reaction. You give me something I value at say a level of 5, by Equivalent Exchange I should get back something you value of at least a 5 or higher. It's a law of the world in Fullmetal Alchemist and the central mantra behind their Power System, Alchemy. In order to use it, Alchemists must study and learn the chemical composition of what they want to influence, use the appropriate Transmutation Circle in order to make it happen. Alchemy is based in science with a few rules changed and as such is easy for viewers to buy into almost immediately.
3 Worse Than: One Punch Man's Super Power Classification
Don't get us wrong, we like One Punch Man quite a lot, but it's equal parts a Comedy and Shonen series. A lot of the time, logic falls by the wayside so that a joke or part of a fight can get across. For example, the main character, Saitama, is quite possibly the strongest being in existence. And, according to him, this was the result of a difficult but easily doable workout routine done consistently every single day.
Super Powers are the power system in One Punch Man, and they make sense most of the time. But, a lot of them can be used infinitely like with Saitama or Tasumaki and that makes it a bit less complex as a concept.
2 Better Than: Pokemon's Well...Pokemon
Pokemon's Power System is obvious as it is in the name itself. In Pokemon, people fight with Pokemon. The Pokemon use their own bodies as weapons and have a variety of moves or techniques they can learn. People who can skillfully train their Pocket Monsters to be better than all the others are called Pokemon Trainers, and are the "fighters" of this world that use Pokemon as their "power". Obviously, for most trainers, Pokemon aren't tools and it's more of a cooperative system, and that alone gives the System something most others don't have. Pokemon is one of the biggest IP's on planet Earth, and there's a reason why. In fact, there's always so much crossover fanart about the series at any one point in time.
1 Worse Than: Bleach's Reiryoku/Spiritual Power
Bleach is a series that was beloved by many for its unique setting. It was one of the only Shonen series of its time that had a concept so closely linked with death that many fans were drawn to it by that alone. And, as time went on and Ichigo became a full-fledged Shinigami, more and more systems were introduced and stacked on top of one another. Things like Zanpakuto, Spells, arrows made of energy, spirit summoning, transformations, Bankai, and even laser blasts. All of these rely on the "energy" in Bleach called Spiritual Power. It is, you guessed it, another take on "life energy" or "chi" and follows much of the same logic DBZ's Ki does. But, because of how many systems get introduced that use Spiritual Power by the end of the series, it starts to become an "end all be all" resource that can do anything and everything.