SoapUI on MacOS: slow panel/window movements, progressively slower as windows added

SoapUI on macOS is painfully slow to use, mainly in terms of window (panel) manipulation.  E.g.: if I have two or three (or five) test panels open, and try to move them around, it becomes a slideshow.  

• Even moving a single (1) window around is slow, with window movement lagging far behind the mouse.  More windows makes it worse.  This also applies to bring windows to the foreground or background.

I've tried the 'disable the embedded browser UI features' fixes as described => here <= to no avail.  I've also tried various tricks to get SoapUI to use my OS specific Java as provided on macOS, and that seemed to make zero difference as well.

• interestingly, windows like the preferences window that open 'outside' the SoapUI panel desktop seem to be quite performant; it is only the test panels that are herky-jerky to the point of being unusable once half a dozen or so are active

I'm running on macOS Mojave (10.14.5) on a macBook Pro with 16 GB of RAM and an 500 GB SSD.  I've been observing this performance issue on macOS through several versions of SoapUI and several OS updates, so this is not a new problem.

 

I'm using the Open Source version of SoapUI, version 5.5.0.  The performance problem is bad enough that I'd happily pay for the full license to resolve it.  But I've seen no evidence to suggest that this investment would be worthwhile.