All these thresholds are arbitrary, acting like only triple doubles is an arbitrary number that doesnt mean a thing is a bit ridiculous. The only argument Harden has over anyone else is slightly better efficiency numbers, and he doesnt really even have that when you compare him to Lebron. Harden ranks poorly in other efficiency numbers (rebounding, assists, turnovers, etc.). Another argument for Harden is team performance which only looks great if you compare it to the debacle of last season, which btw Vegas thought they would win 54 games and instead they won 41. The argument for Harden recedes dramatically when you look at on/off numbers. LeBron leads the four with +16.7, Russell is second with +12.6, while Kawhi and Harden are both below +2. And while Harden leads in Win Shares, Russell leads in BPM, VORP, and PER. While also ranking better in RPM and WINs. Lebron on the otherhand leads the entire field in WINS and is 2nd in RPM.
Honestly, the case only really comes down to Russell and Lebron when it comes to impact on the court. LeBron could easily win the MVP based on numbers (Harden efficiency, with Westbrook value to the team).