Edited sometime later
Here is a specific test.
I prepared the different elements as transparent png using Corel Draw. But you can use Inkscape, rocket, cloud, fire, etc.
From easiest to a bit less easy.
1. NCH Express Animate
This was the first animation I did in 28 mins approx. I was testing ways to animate the fire of the rocket.
The program is VERY light. It is less than 4Mb!
The result: https://otake.com.mx/Foros/Video/ExpressAnimate.mp4
It took me only 20 mins because I already knew what I wanted by doing the prior animation. I did not pay attention to make the scale or the effects the same as the other test. It is a bit tricky to use because you actually animate inside a composition, and that composition is inside the editing tab. But it is a step that only takes 10 seconds to complete.
The result: https://otake.com.mx/Foros/Video/HitFilm.mp4
If you want a long video, with different scenes, different animations, this is the best option. Each scene will be a composition and all merged in the video editing tab.
I would stick to these two options. They have some useful options like defining a "parent" to another object. In this case, the fire is attached to the rocket.
3. Davinci Resolve
It is a bit bulky, I love the program for video editing; but probably for animations, you have a bit less control than the other two. It took me about 20 mins too, but I did not detail the fire or the monster's jump.
The result: https://otake.com.mx/Foros/Video/Resolve.mp4
Images by freepik.com
The example you are posting is not really an amateur animation, it is simple but has several elements that make it a bit tricky.
You need to sync it to audio.
It has some considerable duration for an animation.
It combines several techniques, hand-drawn animation, tween, and bone amination.
Every program will be difficult or easy depending on the time you invest in.
Synfig could be indeed a good option. The level of complexity is defined by the level of detail you need.
For small animations NCH Express Animate.
If you want to deliver as a video there are some other options to animate, but you need to combine them with drawing tools like Inkscape.
HitFilm express, Davinci Resolve which has some basic animation tools, or even Blender.
Another option is Open Toonz.
You probably need to make divide your project into small animations and edit them later.
But you need to define the scope of the results you want. Do you want to sync to music for example? Do you want to animate for the web, or for video? do you want some loops only?
Actually, if you do not need the robot, you could still make some good animations using PowerPoint.
If you want a moving presentation zooming in and out of different parts of a diagram, try Sozi. Another option for this zoom in zoom out animations is Focusky.
You live in the era of video tutorials, take a look at some of them, and download the programs. All I just listed are free.
Which one is easier to use, a screwdriver, a hammer, or some pliers?
The easiest one to use is PowerPoint, it has a familiar interface, you can import a ton of formats, and it is fairly intuitive. The 365 version of it is suitable for animation where you have changes in position, rotation, and scale, as the overall result your example shows, mainly using the Transformation transition and the animation panel, but in order to do the "moving smoke" for example, you need probably another additional tool. It is not free but you most likely already have it.
One with a lot of tutorials is Hit Film, it has a friendly community on its own webpage forums.
You need to enter the video editor, and then make a new composite shot.
And start animating stuff in this panel
If you do not have many elements at the same time, use Davinci Resolve. Here is a quick example: https://video.stackexchange.com/questions/30037/how-is-this-doom-eternal-still-picture-to-stretching-motion-video-produced/30041#30041
Blender is the most powerful of them all and has even a stack exchange forum. But it is not the "easiest" one... until you are used to using it.
And some others are good, but have a small fan base, so, regardless they are good (and probably easy), it is harder to find tutorials.