After 3 times formatting and tweaking my pc system and ESO in ini file sadly have to say any DLC - content needs a overhaul in 3d model department of 3d max or any other software what was used.
Thief DLC - Linking 3 pictures as example with spots that needs to be reworked and rendered proper.
Dark Brotherhood - Linking few spots
Only the DLC content is affected by this what needs texture overwork form the current state.
Well m8 I just keep now avoiding the DLC content cause it kills any immersion running around seeing 50% of stuff black is kind of killing the fun.Its clear that needs to be remodeled in any 3d software maya,max or blender what ever to run proper. Another one I find questionable is about parameter settings what they put for said textures. Cause the NEW added stuff Is off place displaying and like its not part of game.Like its made in 2000x1000 resolution and higher not intended to run below 2000k. Any other content I been playing besides DLC looks nice polished without any disruption. Rest FPS drops I had was in windows settings problems even funny game was not added to windows firewall had to add and other windows settings I had manually to perform tweaks.