A viable BH team in Arena ? Perhaps even more than viable.

Enemy sion + Nihillus means that if you debuff the first, nihillus gains tm and increases your cd. And current meta is full of this duo. Traya also makes an appearance moe and more.
NS, JTR will outspeed you.
Zolo can shut you down.
IMO "viable"has a different meaning. BH are about as viable as murderbears - sure they can win some teams on offense, but not all.