Riki support is great
I'm currently 13W-2L with riki pos4 at 6k mmr. I struggled to win with other heroes, but for some reason riki just wins a lot of games.
Slashers way also coincidentally made a video two months ago and reached 7k spamming riki: https://www.youtube.com/watch?v=hGgMvCDAtqo
So overall it seems like riki has a lot of merit.
I personally don't have a good reason why he's such a good fit for the meta, but he seems to counter a lot of popular picks. Spectre can't find you with ult, Alchemist stuns himself with cloud, Dawnbreaker hates landing into a smoke, etc. The only uncertain matchup i haven't played is Riki into BH.
The item build i've ran is treads+diffusal+shard or boots+vlads+shard. I'm sure you can build other stuff, but these two i find best. Usually followed by a rod to keep enemies in smoke or lategame basher to penetrate BKB. 4k gold items are basically out of the question as you will play on poverty mode every single game.
My gameplan for earlygame is to trade hits and body for my core. Riki has high armor so he's very efficient with tangos and salves. I always get oov, grenade and branches. I place an observer to snipe couriers with E before game starts. Riki is like slightly below average in terms of laning, so don't overplay, help with denies and all that jazz.
Once i hit 6 i place some deep observer near enemy base and go slaughter chickens. This is great for delaying timings, making space and giving your team gold.
My main job is to just help in fights by smoke clouding the right-clicker or essential spell casters. Smoke cloud can also cause enemy to miss on allies inside smoke, idk if this is a new thing or not? Either way it serves as a great save too. Riki pairs well with phoenix egg and magnus RP in my opinion.
So yeah, great hero. I can't seem to win games on BH or Nyx, but Riki just seems like a better vision hero in my opinion. Feel free to ask me anything.