I'll have to agree withe this. However...
I think I'll have to disagree with this...
I currently own four fretless basses - and a bunch of fretted ones, too. Three fretless ones wear flat wounds; one wears tapes. All of them "mwah" quite satisfactorily. And, for the record? They're left handed basses, and they "mwah" just like right handed ones...

They are;
1. '93 Fury Anthem lined fretless. 32" scale, with a Pau Ferro fingerboard. It was built to use tape wounds
only (don't ask how I found that out...), and to sound as much like an upright bass as a medium scale electric bass can. With it's Roto TruBass 88's? It certainly does a good job... The strings are as low, and the neck is as straight, as I can get away with. I use the same finger technique as I would with an upright; it "mwahs" as well as the Roto's (comparative) lack of sustain will let it. I was... disappointed with the Pau Ferro fingerboard initially; it's comparatively soft for a fingerboard, IMO. But, the more I play it? The more I think the choice of Pau Ferro was deliberate, and the softness contributes to the upright vibe... TBH, the bass was very well played when I bought it, and although there
looks to be considerable wear? I can't really
feel much...
2. '24 Birdsong Fusion lined fretless. 31" scale, with an Ebony fingerboard. All Birdsong basses are 31" scale, and unless you specify other strings? They ship with the long scale
only D'Addario ECB
82 Chromes. I don't use D'Addario strings if I can help it, but Birdsong's owner assured me that the basses - and their proprietary pickups - were built for those strings. So, that's what mine came with. Again, the bass is set up for low action/straight-ish neck. Does it "mwah"? Does a cat have an ass? The Chromes have a lot of sustain, and the "mwah" to go with it. And, this is a
short scale bass...
3. '24 Schecter Stiletto Studio 4FL lined fretless. 34" scale, Ebony fingerboard. It came from the factory with Ernie Ball Group IV Flats. Again, low string height/ straight-ish neck. Other than being a little more flexible than the ECB82's - and a little less bright? Plenty of sustain - and "mwah"...
4. '24 G&L Kiloton lined fretless. Custom Shop, since it's a lefty; 34" scale, Ebony Fingerboard. It came with some kind of rounds - probably D'Addario EXL160's - which lasted about 5 minutes past the initial function check. Did they "mwah"? Yes they did. And, to my nerve damaged, frostbitten fingers; did they feel like a wood rasp when they did? Why, yes... yes, they did. They got replaced - very quickly - with a set of La Bella LTF-4A Low Tension Flats. Nicely flexible; good sustain; and they also "mwah" quite well. The Kiloton is set up like the other fretless basses are, and TBH? It's the one I play pretty much like I play any of my fretted basses - most of the time...
Honestly? I don't get the obsession with "maximum mwah". Just like I don't get the obsession with sustain. Yes, I have several basses that can sustain 'till the cows come home. But... who in the Hell
needs that much?!? Even the basses I own that sustain the least, have enough for the songs I play with them. As for the basses I own that sustain the most? That's not a feature, AFAIC; that's a failure... And I'm afraid that that goes for "mwah", too...