I watched the video; this is not like what I experienced: He is able to stabilize the rocket more easily.
After some investigation, I cannot guarantee that the problem is not related to my hardware (which is not very powerful). I tried it a few times and every time the experience was slightly different; sometimes better, sometimes worse. Perhaps it takes to long to process the key presses, which are than interpreted incorrectly as a consequence.
I tried playing with and without timewarp on; it made no difference. I could easily spin the rocket in both modes unintentionally .
In my opinion, it is not a bug in your game; more likely that the system dependent input latency plays an important role here. Perhaps a way for the user to adjust the acceleration combined with limiting the maximum rotation speed as well as a different ease-in ease-out design would prevent this problem. This could also solve the complaints about being to sluggish.
I had a similar problem with my last Godot game: I got a lot of complaints that my main character would be way to slow. Partly, this was intentionally and by design. But after watching the streamer's footage, I realized that my game behaved quite sluggish on his system (even though his setup was way more powerful than mine).
If I may ask: On which operating system did you run your Chromium? Because for the testing, I was using the Manjaro flavored Chromium build under Manjaro/Archlinux. I had this issue with my last game that on some operating systems, it would run with Chromium and on others (with the identical Chromium version) it would not.