Elongated shapes/polygons flickering over texture

Mainly they aren't such a buzzword anymore is because new features like adaptive tessellation make total polygon counts less significant. If the game is optimized well when a character or item is only a couple of dozen pixels onscreen then whatever amount
of polygons are actually needed to maintain the profile and texture coordinates is actually really low.

Also more advanced texture shading features like parallax mapping can use textures to give flat one polygon surfaces the appearance of being tens of thousands of polygons. Couple this with better lighting systems that also help create the illusion of a complicated
surface sometimes faster and more convincingly than if you used a lot of polygons.

There is still a huge amount of room of improvement of how many polygons can be rendered. Currently to render things like foliage you use simple flat sprites or a square polygon with a texture that is transparent to show leaves and blades of grass. Actually
having each blade of grass or twigs and leaves on a tree rendered as a polygon model would bring the best computer setup to a stand still with just a couple trees and bushes in a scene.

Only type of rendering that has promised to do this in real time is rendering using voxels, but only a couple engines have popped up demoing the tech and then disappearing before use in games. Only game currently in development promising this technique is
Everquest Next and how much it uses it remains to be seen.

I'm not sure I like the textures or the shape of the islands, but I do like that they're flat... and free.

Polygon count is still used. Rocksteady just mentioned that

Characters in Arkham Knight are much more detailed, flexing textures and polygon counts three-to-four times higher than in Arkham City. "One character is as big as the polygon count of Arkham
City - the whole environment," said lead character artist Albert Feliu.

www.eurogamer.net/.../2014-03-05-rocksteady-reveals-batman-arkham-knight-in-detail

From what it looks like in the vid it seems that your HDMI port on the console is failing and you will need to get it serviced or look at a replacement console.

Recommend looking into the steps here:
https://support.xbox.com/en-US/my-account/warranty-and-service/getting-your-product-serviced
to get it serviced.