The linked article states implies they are built:

“These are the first two prototypes — which have already been developed and pre-tested for structural stability and high-voltage performance.”

That’s very weaselly of them.

I'm sure something like this would be doable and I like the idea, but the stag doesn't seem structurally sound for example.

People generally just want cables to be buried, but apparently this poses more problems than just added cost, so companies are reluctant to do it (as far as I understand it at least, I've only looked it up briefly in relation to the Ventilus/Boucle du Hainaut project here in Belgium).

The rule of thumb is that if there's a mention of or a link to the Yanko Design website, you know it's a pipe-dream design concept detached from reality.

Here it features the review by YD, so, yeah, that's not just not built, it's not buildable in principle :)

It does. That was my first thought. Buried AC cables are not cost effective, DC is better but still more exprndive than aerial power lines.