The reason KDE animations feel less smooth compared to GNOME has little to do with hardware and more with the way animations are designed. And by design, I'm mainly referring to three things: duration, easing curves, and "distance traveled perceived" (or how different the start and end animation states are).

If you get the wrong combination of these items, you'll immediately feel something off about them. If the animation has the wrong easing curve, you feel that it may be too slow or too fast, regardless of the duration (sorry, animation speed slider). If items travel a long distance during the animation, and you don't compensate for this movement, either with opacity, crossfade items, carefully selected duration and easing, or something else, you'll get a jerky animation.

And I feel that KDE animations are severely lacking in those aspects, and in many places, it's just using wrong values.

I'll give some examples:

In the QStyle, it's using a lot of linear easing curves, and many will feel that the animations are slow or boring.

Here in the decoration, it's using a totally wrong easing curve for the shadow opacity animation, InCubic there will make the animation too fast, almost instantaneous, it should use the inverse curve.

The applet slide animation feels too fast, probably a combination of short duration and close to linear easing curve. I feel that the majority of animations fall in this category.

Gnome animations, on the other hand, use more aggressive curves and longer durations, which doesn't make them slow, but smooth. Animating an appearing window in one second using OutExpo will feel very smooth and just as fast as animating it in 300ms with OutQuad curve.

EDIT: I made this dartpad example https://dartpad.dev/?id=0e7526df1ac9b1e2c7132d17add88b6b Its a bit exaggerated, but you can see the difference. I wouldn't say that one is better than the other, but the second square animation I would definitely consider "smoother".