Proper Procedures for Regrading Under a Deck?
Regrading the soil is a must since the soil level was 6" below the rest of the area. The landscape fabric keeps weeds out but not water so I wouldn't be using that. The plastic would have a limited life and you don't want to be ripping up deck planks to check it. I'd be thinking about installing flashing under the deck planks and sloping it down away from the foundation where you think the problem exists. You can get flashing in 50' rolls 20" wide at most home stores. Hope this helps a little. Good luck.