Treant was added back to CM mode in 6.72 or 6.73. The ulti was nerfed slight, now only 3 seconds duration.

The scary part of Treant is not the ulti but the invi skill. Allow you to walk through wards and gank.

Treant is not a hot/common pick in DoTA CM game. I was in Gamefest tourney and no one picks Treant. I think the problem lies within he is more towards a support hero but all his skill consume a lot of mana and he need some items before he can perform, something like omniknight. You can activate BKB after his ulti so you can get away from it, but not activate the BKB before his ulti.

There is always a few aspect why some heroes are not picked oftenly, like can they push, can they defend, can they war, can they lane? Treant is something which can war but laning phase going to be tough for him. Since DotA 2 is more towards push, taking towers, I guess he will only be picked against push strat because of the global armor and heal to towers but people can counter it with night stalker which make that skill kinda useless during the night time.