Why did Troll storm into the pro scene?

I did say he almost *could* be :). Think about it, a good, cheap, long ranged slow, decent harassment...and that ult as a pure teamfight/pushing boost for his team. It's just so strong, especially if your team hit hard but lacked attack speed.

Ultimately, I'd agree, he's not really there and he's better in a carry spot, but it does make you think.

cof cof 6.83 max atack speed was buffed cof cof

Even with Fervour and Battle Trance, Troll doesn't normally reach the cap (not even the old one), this only really affects Windranger and Ursa

since guide adv is not allowed,

Maximum DPS Calculation
Troll Warlord's items : Daedalus, Satanic, Monkey King Bar, Butterfly, Mjollnir, Boots of Travel.
attack speed:136(from Fervor + 180 (from Battle Trance) + 68.75 (agility gain per level) + 21 (starting agility) + 9 from taking stats + 15 (MKB) + 60 ( Butterfly) + 80 ( Mjollnir) = 570 attack speed (30 away from maximum value)
BAT = 1.55

Attacks per second = (1 + 5.7)/1.55
=4.3 attacks per second

Just to be clear, the reason he's picked has nothing to do with Battle Trance. People USED to pick Troll as a ultility/walking ult hero back then in the TI3 times when his ult was stupidly good and had literally no cooldown.

Then, his ulti got nerfed to decent-but-not-great level, and Troll fell out of the meta completely.

And then, he got buffs that make him completely OP as a right-click/racecar carry, since now he's literally a carry with a permenent haste rune who attacks with NATIVELY maximum attack speed (especially since the latest Fervor buff) and bashes enemies for 2 seconds on hit. Oh and he has improved base attack time on top of max attack speed, nice balance Icefraud. This means that the only thing you need to build on him is survivability items and a disable, you don't even need to build damage! This hero with a skadi and a SNY or blink sits at 3.5K HP, is completely unkiteable and deals tons of DPS while any other carry with that build would deal no damage.

People really play right-click Troll, not ulility or pushing Troll. Support Troll COULD work because indeed you can buy low-cost stuff on him like drum or blink, but that's kind of the old "walking ult" meta, now he's really a safe lane carry or a mid hero. A bit like how people play Juggernaut, he's just a carry who runs fast and hits hard...except that unlike Jugg he also has a billion HP.