With Ant-Man and the Wasp: Quantumania teasing multiple Kangs in it's credit stinger, it looks like the Avengers are gonna have their hands full. The current line-up, as scattered as the potential Avengers recruits are, appear to be no match. However, just like the threat of a singular enemy like The Sentry (which can be read in Part 1) the threat of Kangs can be overcome, as is seen in other movies.
Other MCU movies that have large armies, that often are faceless, are the Chitauri and Ultron bots in Avengers and Avengers: Age of Ultron respectively. Although both overwhelmed the Avengers, the armies were beat either way as the aliens and bots weren't that powerful individually. The same can happen with Kangs, were the majority of the Kang army aren't that powerful and thus easy to beat. Either way, an army of Kangs will have to be defeated. And the army can still feel threatinging.
The magic red button
One way a large army can be defeated, is through the use of a magic red button: a (metaphorical) button is pressed, and the entire army is destroyed or disabled. Such a concept can be seen in The Rise of Skywalker, where the Xyston Fleet is easily defeated when the Resistance blows up the one signal tower controlling the entire fleet. Although the tower is not a button, it is a singular objective for the heroes to aim for. However, if such a large army can be defeated so easily, it lacks any real threat.
Another solution to the magic red button is that is has a narrative undertone. In Total Recall, there is the faceless cop army that has to be defeated in the third act and is done so by blowing them up in the train inside the tunnel. The tunnel itself is a symbol of oppression that also has to be destoryed to gain victory, and thus offers a solution to the army that has to be defeated. For Kang(s), the magic red button could be anything, but can be more compelling if it also has a function besides being just a red button.
The looming threat
To make a large army feel threatening, is to set it up from the beginning. The enemy could even overpower the heroes at first, or leave a mark that makes the heroes realize they cannot take the fight straight to the enemy. Instead, the heroes go on a journey. This can be to find more allies, to find a bigger fish as the enemy, like Kong in Kong: Skull Island, or something else. They journey as such becomes the focus of the story.
In The Lord of the Rings, it is established right away Sauron, or rather, his ring, has to be destroyed to stop evil from taking over. Although dropping the ring in Mount Doom is a magic red button, they journey there instead takes over the story. The same happens with Thordak in The Legend of Vox Machina. Gathering vestiges and allies is the focus. Both villains are overpowering at first, but can ultimately be defeated. For Kang('s army), the same applies. Whether that is tools, allies or a bigger fish needed to defeat them.
Antagonistic forces
By setting up a threat right from the start, also give a sense of urgency to the story. Such can be seen with the Reapers in the Mass Effect trilogy. The first game doesn't actually reveal the whole threat later on in the story, but sets them up as big threat for the rest of the trilogy. And when they arrive in Mass Effect 3, they are indeed an overwhelming force. Only through gathering allies, the threat can be defeated (depending on the player's choice).
Finally, there doesn't even need to be a face to the entire threat. Not to the enemy army, or the main enemy itself. In Top Gun: Maverick, the antagonistic force instead comes from forces pushing against the heroes' journey. Whether that is in training, character dynamics, or the unnamed enemy country. And conflict between characters can be seen in the MCU as well, as Steve & Tony in Civil War and the Guardians in the Guardians of the Galaxy movies shows. Kang does have a face, but as these movies show, the villain doesn't have to be present to make it's presence felt.