"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.
Normal attacks in RPGs. Special moves and magic are a lot more flashy and generally much more effective, but they are usually restricted by something or other (Mana, Limit Break, etc). And some spells might not even work when you really need them. Normal attacks usually cost nothing at all to use, and have no cooldown or speed penalty.
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. Workers are also used as early-game scouts due to starting the game with several of them, and having a very low cost per unit.
The buildings they construct also qualify, as they simply sit in place and produce what you tell them to. Resource buildings especially so, as they often have a very basic design and no functionality whatsoever, but if you don't build a bunch of them, you can't have an 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.