The Marvel Cinematic Universe is filled with some of the strongest superheroes and most dangerous villains in movie history, with alien beasts, Asgardian gods and gamma-irradiated giants leveling cities during the course of their battles.
And then there are the tiny, fragile little beings who are just doing their best, despite being almost laughably weak. Now, that's not to say these characters aren't wonderful, charming, sinister, or downright awesome for what they contribute to the world. It's just that, if they tried to punch Thor, they'd just break their own hand.
In a effort to give them their due, it's important to understand what they contribute before explaining exactly why, despite their various mental or emotional strengths, they are physically out of their league in the MCU.
Justin Hammer is supposed to be a parallel to Tony Stark - he's a wealthy, megalomaniacal arms dealer and tech CEO who builds Iron Man-like battle armor. However, he's more like a poor man's Tony Stark instead of a mirror image. While Tony is egotistical yet brilliant, Justin is just a self-obsessed buffoon more interested in money and self-promotion than helping the world or even producing a competent product.
There's one telling scene in Iron Man 2, when Justin has Ivan Vanko sitting in a room under armed guard, and the well-dressed businessman is doing his best to threaten the Russian lunatic. Justin tells Vanko that he's "a dead man" if Vanko doesn't do what he wants. He's putting on his toughest tough guy act and it would be physically impossible for Vanko to be less concerned or intimidated. While he has an undeniable flair for salesmanship - which he displays while selling arms to Lt. Col. James Rhodes - he's just a weaselly jerk in a grey three-piece suit.
While he is known to the world as the Mandarin, a global villain of unequaled magnitude, it's eventually revealed that the international baddie is just a washed-up, substance-using actor named Trevor Slattery. He was hired by the evil think tank organization Advanced Idea Mechanics and the deranged scientist Aldrich Killian, who uses the Mandarin's supposed attacks to further his goals and cover up accidents resulting from his various Extremis program mishaps.
While the Mandarin has built a fearsome reputation through menacing propaganda videos, his true, drunken, oblivious persona is revealed by Tony Stark. Instead of the psychotic villain Tony expected to find, Trevor turns out to be a scared, idiotic actor desperate for work who has no idea that he is a very public pawn in a vast conspiracy.
Also known by his awesome (but not particularly intimidating) real name Phineas Mason, the Tinkerer is a construction site salvage worker turned clever, brilliant inventor and underworld mastermind in Spider-Man: Homecoming. Working with Adrian Toomes - AKA the Vulture - Phineas is able to use salvaged alien and Ultron technology to create hyper-futuristic tech to aid in heists pulled off by Toomes and his bitter crew of former upright salvage company employees.
While the Tinkerer has an incredible mind for reverse engineering and modifying otherworldly technology - and developing anti-gravity blasters, shocker gauntlets, and matter phase-shifters - he doesn't actually use any of the tech himself, and basically stays out of fights altogether. He's an affable behind-the-scenes kind of guy who's good at welding and stays in his own lane.
Very few characters in the MCU have been as important and influential as Hydra scientist Arnim Zola, while still being so incredibly non-intimidating and weak. Working with the Germans and Hydra during WWII, then spearheading the Winter Soldier program - which leads to Bucky Barnes being reborn as the metal-armed assassin of the same name - so much of the MCU's history, and even its present, is steeped in Zola's villainous machinations.
That being said, he's a sniveling, pint-sized jerk who sends others into battle to fight on his behalf. Despite inventing superpowered exoskeletons, he never tries to don one himself because he's just a frightened inventor with a love for hate. Eventually, he perishes of a terminal disease, but his brain and consciousness are transferred and downloaded into a massive computer in a bunker beneath Camp Lehigh.
But even then, his intelligence isn't loaded into a giant robot body (as it is in the comics). That could at least pose a threat to Steve Rogers and Natasha Romanoff when they discover the computer during the events of Captain America: The Winter Soldier. Instead, he's just an antique reel-to-reel computer, and all Zola can really do is stall the pair long enough for S.H.I.E.L.D. to try and blow the base up. Even this plan fails, as Steve and Natasha manage to escape, while Zola's mainframe is finally obliterated by the explosion.