LR, from what I was told, DOES use a sort of scratch disk, though not in the same way as PS. It uses it to cache aspects of the program and file you are working on. But no, not a scratch disk in the same way. I also read the article about doing all your local edits and THEN doing your global adjustments. Stupid approach. But the reasoning was that for any local adjustments you make, LR then has to apply all the various global adjustments as well.
I think the way LR was written, there were never supposed to be local adjustments. It was supposed to convert your RAW files, based on global edits, and then anything else was supposed to be done in PS. Short of a complete re-write, LR has been painted, somewhat, into a box. I can't figure out how Capture One can do a lot of similar things (though granted, for me, not as easily and straightforward) and not grind to a halt. My 5Ds are the benchmark for me. Capture One flies through them, by comparison. But I still like many of the results of LR better and so I still with it.
I also find turning on GPU support is almost detrimental to my performance. I have NEVER, on any of my three computers, found it useful.