IMO, "ergonomic" is in the hands of the wielder (eye of the beholder, etc...).
I don't think I can agree with this... The weight IS the important consideration - no questions. As mentioned, EART was sold cause it had "normal" weight instead of ~2,5Kg of *S., which I felt uncomfortable when both standing and sitting. So for the player who performs almost exclusively standing sure, it equals ergonomic. But this is probably what, 1% of all guitarists? I'd argue less than that!
Given that, I wonder why headless is a consideration for you - is it ease of travel?
I'm playing sitting most of the time, like 95% of time or even more, like this:

What do I get:
1. Exactly same guitar-to-body position when both sitting and standing - saves a lot of practice time!
2. Perfectly straight, "normal" body position, never twisted as it would in "rock-n-roll" position or even with a normal guitar positioned as in a picture. And if I want to change a position with this guitar, like sit in a deep soft couch or high bar stool, it's still WAY more comfortable than a guitar with "usual" body contour. Well, the image above says it all, actually. He sits so comfortably like there is no guitar at all.
3. Left hand position is in much more "normal" position and less twisted than if you'd put K in same position against your body. Same goes for right hand, it's more relaxed cause it's lower than with usual guitar in same position.
4. I never afraid of kicking someone in a face with headstock in small bars

Did that a few times - still sorry for the boys :/ Kids don't afraid to approach me from the left side either

5. It's very comfortable to sit like that in front of the computer. I'm typing this while sitting in "ideal", i.e. recommended body position against the table and a computer, and my guitar sits comfortable on my left lap. I never have to pull it down - NEVER. This alone makes it worth it's price, TBH. Normal guitars would not allow you to work with keyboard for extended periods of time without the need to put it down or twist your body to keep it from falling forward or to the sides. I can keep playing it while I think what to type next or waiting for someone to answer or whatever, you got the idea.
So this is my definition of ergonomic. Again, I agree about the weight, but *S is already significantly lighter than my cheap Peavey strat or gold top Gibson which can be used in a gym for powerlift training.
This said, I don't like *S right hand support either! But because of it's body contour, I can push the neck slightly forward when sitting, which makes left hand position even more comfortable, and mitigates the lack of right hand support almost completely. I realized it is so comfortable that I tend to do it while playing standing too.
And, finally, Kiesel lets me move the dumb control locations
I moved volume knob to the tone knob position and removed tone control at all

I also reversed the pickups switch because I usually use neck pickup. Now that it is in the lowest position, I rarely kick it

You can see it in the image above.
didn't bring up the S neck - I actually kinda liked it, but I wasn't sad to see it go either)
I don't really care about their neck either. And don't get me started how bad their neck-to-body joint and access to the high frets!!!