"Of all the weapons in the vast Soviet arsenal, nothing was more profitable than Avtomat Kalashnikova model of 1947. More commonly known as the AK-47, or Kalashnikov. It's the world's most popular assault rifle. A weapon all fighters love. An elegantly simple 9 pound amalgamation of forged steel and plywood. It doesn't break, jam, or overheat. It'll shoot whether it's covered in mud or filled with sand. It's so easy, even a child can use it; and they do. The Soviets put the gun on a coin. Mozambique put it on their flag. Since the end of the Cold War, the Kalashnikov has become the Russian people's greatest export. After that comes vodka, caviar, and suicidal novelists. One thing is for sure, no one was lining up to buy their cars."
... and, working backwards through history, healers in almost any pencil-and-paper roleplaying game.
Same for medics in FPS games that have them. More importantly, ammo limitations, rate of fire restrictions, or other factors often make normal guns more useful than sniper rifles, power weapons, or the BFG.
Similarly, weapon loadouts that don't require much ammunition or allow you put a ton of ammunition on your vehicle in things like Humongous Mecha combat sims. The bigger guns tend to be unable to stock much ammo and take up more space, besides.
In platformers, Goomba Stomp or basic moves, as opposed to the things you can do with powerups. Vital since the said powerups aren't always available, and if you lose yours mid-level, what then?
In strategy games, the basic combat unit is usually more efficient than the larger (and cooler looking) counterparts. Tournament players will often make heavy use of rather basic units in general. Any type of rush depends on this trope.
Again, in strategy games, Worker Units. These guys have little or no combat capability and present easy targets for your enemies, but without them, you have no economy, and without an economy, you have no army.
In an extention to the worker unit the buildings they construct are also this trope. All they do is just sit where you build them and produce what they were made to do. Resource buildings are especially boring since you typically can't command these things to do anything and you have to build lots them to maintain your army. Resource buildings also tend to look really dull and mundane compared to other structures. Just like the workers without your buildings you have no economy or army.
In Card Games, simple and resource cheap cards often reign supreme, with efficiency being more important than raw power.
This is often particularly true when button combos are required. By the time the new moveset is unlocked, the enemies are too powerful to take lightly by practicing your new attack on, and your own damage output is high enough that failing to activate your new ability will simply kill a mook outright with a mere jab.
The Jack of All Stats can often be this trope; they may lack the coolest, or strongest moves, but are fairly good at most attributes, and lack the glaring weaknesses of other character types.