Hey Silvio, yes it is… I’ve experimented with quite a bunch of downscaling algos from OSS to expensive tools and personally I always find Sverlov’s the best, in the sense of balance, specially regarding granny images (I’m a sucker for texture). I use the microcontrast one and very seldom other sharpness than zero. I’ve used it for years; recently made new tests with huge phase one’s files and despite that (for instance) progressive downscale+added sharpness produced more eye catching images (razor look), C3C was reassuringly consistent through very different textures, shapes, hues, etc.
Unfortunately you’re right, C3C only runs inside PS. It feels a bit like an insult in such a place as this, but - as pimps as adobe/apple/and the kind have become - I’m a PS user for almost 2 decades… and it comes a time when you just know it (the good and the bad) and so I get to my final image 10 times faster than in other platforms. With LR even faster. For my non paid work though I very much enjoy exploring and getting to know (and admire the work in) such powerful tools as GIMP, photoflow, GMIC, Darktable and so on.
I have my own aesthetic theories, borned from actual doing, about video being closer to painting and photography to drawing… but that’s for another day maybe 
Thanks also for the heads up, no-halo it’s what I normally use in GIMP
, but again (and sorry for repeating) tested it against C3C and quite prefer the later… maybe it just has more to do with my heterodox workflow; I do appreciate that you pointed that out, peace.