This is a very old issue with Godot and due to its inconsistencies, I'm inclined to believe it's related not to the program lagging or having the wrong PC specs, but due to how Godot renders with different drivers and desktop environments.
It's not a problem exclusive to Godot either, other engines have issues with visuals hitching (both in 2D and in 3D), and it's just as inconsistent there. Desktop is generally just not a very friendly place for smooth gameplay, you'd want a device that's specially built for that purpose.
There was a fix pushed in master that attempts to help solve hitching with physics bodies, just one of numerous causes of visual hitching. Supposedly there's another issue related with how Camera2D works, and so by manipulating the viewport yourself, you may be able to solve some hitching. I've personally noted that different compositors can cause different levels of hitching (with buttery smooth--albeit tearing--gameplay with no compositor at all.) Some say turning off vsync cures visual hitching, others say it doesn't.
Not only is the problem inconsistent for different machines (hence some saying it's a big problem, while others saying they just don't see it), it's inconsistent when it happens on those machines affected; it may not happen at all for a while, it may happen a lot for a while. You think it's fixed because you changed X or Y in your code, but it comes back eventually.
Anyway point is, don't bother wasting your time trying to find something wrong with your own setup. I made one game that was extremely jittery on my own machine, but everyone else who played it said it was very smooth on their end. If there's a solution, it's going to be in engine code I think, not on the game developer's end (nor should they be concerned about this; after all, the engine is meant to get this sort of stuff out of the way for developers.)
