The fluidity is about keeping activity on the screen tightly in sync with motion on the trackpad and having zero or no unexpected behavior or jank when e.g. reversing a motion partway through to undo it (say, starting to slide three fingers up to expose all your windows, stopping to peak at something, then sliding them back down to put everything back where it was—you can even stop in the middle of it to make the windows do a little dance and nothing goes badly wrong or far out of sync). It nails that stuff even on my aging low-specs-even-at-the-time 2013 MBP. It's not so much about raw UI speed which, yes, light Linux/BSD window managers still hold the crown for (outside dead or niche operating systems like BeOS and QNX or maybe even old versions of Windows, which actually hold the crown)

BeOS lives on in Haiku (https://www.haiku-os.org/) which is both still alive, and blows most "light Linux window managers" out of the water in UI speed. :)

I have a VM with Haiku and I can confirm it is indeed very fast.

I am no Haiku expert but the Haiku's window manager does not support window composition and does not use GPU acceleration, right? It is also not modular and cannot be replaced.

You can disable composition on XFWM and make it run a little faster on lower spec hardware. You can also use a WM like i3, Windowmaker or Enlightment.

IMO, XFWM is the right balance between functionality and performance.

The whole point of Haiku is a holistic approach to system design, so no, you cannot easily replace the window manager. You can, however, write "decorator" plugins which draw different window borders, write shortcut plugins for "tiling", etc.

It indeed does not use GPU acceleration; Haiku as a whole does not have 3D drivers either (but there are plans.)

It’s honestly pretty bad on their slower and/or older models - they’re pretty clearly developing for what their devs have, which is their higher-spec machines. If you go into an Apple Store some time and play with their higher-spec machines it’s pretty good.

True. But what happens when you run XFCE in one of those higher spec machines? the advantage remains.

Perhaps this is a UI preference difference. I like the animated views on OS X and the speed seems acceptable but there are definitely browser apps (like the Chase website) where things animate in slowly and I get frustrated. So perhaps we're just differently placed on the curve.

Does it? There's a limit to how "snappy" XFCE gets.

I think this is the "animations vs no animations" argument, maybe - I like them as they give context to my actions, but I imagine some people don't.

For nice widget animations you can install a GTK engine/theme. There is a deluge of GTK themes you can choose from if that is your thing.

There are many themes inspired on macOS if you are aiming for that kind of look.

http://reddit.com/r/unixporn has a lot of that stuff. You can just go and grab someone else's configuration and apply it to your system.

If you are aiming for window effects with no regards for performance, try Compiz. You can add as many window effects as you want.

Sure, but when you add those animations to your setup, do you perceive it as being slower?