This hero along with Drow Ranger is very popular and strong in public matches.
How come this hero isn't being picked or even banned in tournament matches?
A carry's potential (arguably) is gauged by his/her ability to stay alive.
Examples: -Spectre's dispersion gives her great damage reduction, both physical and magical.
-Medusa's mana shield gives her significant damage mitigation. With proper item builds, she can be very difficult for even a group of 5 to burst down.
-Faceless void's Backtrack has a chance for any incoming attack to do absolutely no damage. He can also bash enemies, and a properly placed Chronosphere freezes them in place for up to 5 seconds, guaranteeing his survival for that much longer.
If we look at Huskar, he has significant burst potential with his ultimate, and great sustained damage output. However, this is only considering he is allowed to continue attacking. His sustain skill is his single heal spell, which can be extremely unreliable as it relies on being on low health for it to be most potent, and is completely countered by Ancient Apparition's ultimate Ice Blast, which prevents enemies from healing, and instantly kills them if their health falls below 9/10/11%.
Drow is similar to Huskar in that she has the potential for extremely high single target damage. However, she has very poor STR gain, making her squishy. She is also slow and has no escape skill making her very easy to gank. With her ultimate, Drow ranger does get a significant boost to her armor, however the recent update removes her ultimate's buff when an enemy gets in close range. Also, having more armor does not mitigate magic damage, so heroes like Lion and Lina can easily kill her.
Because he needs to be low hp to do dmg and single stun kills him. Current meta concentrates on aoe and disables. He only good in pubs where people don't play organized and where he can gank a lot.