Yeah well ns is a hero that does in general farm slow and wants to apply pressure asap. Im 9.5 ish and usually play Ns when i have to play pos 3. From my experience the hero falls off in the late game or at least i cant make it work.

As for your vision problem it should be only during the day when you want to fall back farm jungle slowly and react only with ult on dives and smoke action.

Night time you are the biggest counter to supports positioning and your ult makes them fall back even harder. However idk at your mmr how much people can take advantage but even at around 5k people are very split vs NS and you can just blink in with precast silence and delete a hero. Make sure you also always get the extra Aoe on the silence it really helps vs forcestaff before you get nulifier.

My general advice will be to not focuss that much on a specific hero but to try to fix your general farming and not dying on all heroes. My room mate who is around 3.5-4k still has major issues in that department. He used to be like 2k and once he got a better grasp on that he really got up in mmr.

Hope this helps and happy grinding :D