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And the ironic thing is that neither "modern" D|S nor "modern" V4.1 can deliver one iota more realism over "ancient" Poser and V3.

What does any of that matter? You want realism, go hire a model and take some pictures.

I'm not going to argue about D|S vs. Poser because frankly, I have only a marginal interest in either, at best, and if they both went belly up, I'd not likely miss either of them.
But V4 is a much more versatile mesh than V3. It's more dense, and the points are arranged better for morphing. Maybe that's not so evident with Poser's crap morphing tools, but take it into LightWave Modeler, modo, or ZBrush (or any quality polygon modeler) and have a look at what's possible.
Not just that, but the density of that mesh creates more points, allowing for more detail in the maps, considering the textures are interpolated between UV points. More density equals more detail, and allows for more even morphing with less texture stretching.
Yes, it's more complicated, but so what? Really, why does it matter to you? You said you'd like to like V4... ("I WANTED V4 to be good.")... but the argument is it's too much to deal with. And yet you go on about how thoroughly you understand all this rigging and joints and so on. Look at it as a challenge. If you're such an expert, it shouldn't be a problem. If you want to like V4, by all means find the things about it which allow experts such as yourself to go to town on it.

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Now with V4.1 the bodyparts are scaled all over the place. Result: Without buying a full fledged 3d painting program it is impossible to create a proper V4.1 texture without noticeable seams.

You say this as if it were a bad thing....
Well, I bought two full fledged 3D painting programs - Deep Paint 3D a few years ago, and more recently, Body Paint 3D, standalone version.
3D painting on a mesh is a hugely more productive thing, for me at least, and many in the professional CG animation world, for that matter, than painting in 2D, and I can tell you 3D painting on a V4 mesh is far, far easier and less frustrating than painting V3.
Of course, both those programs allow you to switch back and forth between 3D, 2D and projection modes.
It's a large part of where texturing for 3D characters is headed in the future, and V4 is more than ready for it. In 3D painting the density of the mesh is even more important, as the interpolation of the "paint" between vertex points  is more apparent. That's why you switch back and forth between modes and projections.
So Joe AverageTextureguy can't easily paint a good texture for V4 in Photoshop. My heart bleeds for him and the loss that means for the community, really it does.

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I predict there will be A LOT less (If any) V4.1 hybrids out there, and a lot less free V4.1 textures.

Nope, DAZ started a race for the bottom line, because that's where they think the money is.

Oooh, the big Evil DAZ trying to make a profit while sticking it to the little guy. It almost brings a tear to my eye. Lord, I love this country. :)