Stone that thick isn't any weaker than your average ceramic tile I'm sure. What is going to happen to a solid screed that effects stone more than any other tiles? I think it's pranoia. I can see it with Ufh as there is some expanding and contracting.
I have tiled many natural material floors without heating, and without uncoupling, no problems.
Fitting 70m of uncoupling is a significant amount of money!
Well I'm pleased for you, and if it's worked for u that's great.
But we're all entitled to our own opinion, and if they didn't differ, this forum wouldn't exist.
And I'm sorry that my opinion differs to yours, but it is my opinion nonetheless.
As far as considerable cost goes, on a floor that size, in terms of a percentage,
I can't agree!
Nice images, but proof of install isn't proof of longevity.
And I've read no confirmation that this particular material is 20mm+
and if it is, even more reason to protect your investment.
But it's just my opinion.