I wouldn't be too sure since it came up in the book as opposed to the sets. The books are notorious for having little oversight in terms of editing (at least from that period).

As such, that could be a detail Scott and Cory added.

News flash: In the most recent uncharted realms Nissa pretty much stated all planes have leylines.

Also that the leylines associated with life on Amonkhet were pitiful and sickly.

Actually, this is the second (third?) time she has come across cursed leylines. She had issues with the leylines of Innistrad, and things went sideways for her in Origins when Lorwyn switched over to Shadowmoor as well.

Amonkhet confirmed to lean towards ?

I would classify a desert of the dead as a area. It's got winds () and hot sands () for sand storms, and underneath all that sand are countless undead () ready to burst out of the ground and eat you.

It'll be interesting if all the life energy is concentrated under those magical domes that shroud the more civilized areas.

I say (in more or less that order), since the suns are an important aspects

Distance is still relevant in the blind Eternities unlike time so it is possible for multiplanar cultures to develop.

The leylines on amonkhet are possibly tied to the gods. Since Bolas killed some, the plane has started to wither away and become sickly and weak.

The last story also implies that Razaketh is behind the planewide undeath curse, so his influence could be damaging the leylines as well.

As I said in the Story thread, I think you are incorrect or assuming here. It is more likely that Razaketh is responsible for the control of the embalmed as well as being some piece of the afterlife puzzle that Bolas put into place for unknown reasons.

Relevant quote from "The Writing on the Wall":

It's heavily implied that this is Nissa communing with the plane itself. I suppose its possible that Razaketh is subverting that ability to mislead the Gatewatch, but that seems stupendously unlikely.