Probably one of the reasons why Gastrodon was moved up in usage for Gliscor and Thundurus which I am predicting. (Main reasons because of rain and two immunities + reliable recovery and decent stat distribution which people didn't really abuse until now [outside of grass knot, but then who uses grass knot on Thundurus]).
Considering Ground-types are completely immune to Electric attacks, and Grass Knot is Thunderus' best option against them [Except Gliscor]... I'd say quite a few people run Grass Knot on Thunderus. I ran it on my lead Thunderus back when I used one, and it would usually get 2 KO's off the bat, simply because people expected me to carry Taunt because it was a lead.
I mean, there's nothing stopping a NP+ 3 attacks Thunderus, with Grass Knot and HP Ice for Dragons.