You are mistaken about Overflowing Quiver. This talent gives you an extra Whitering Fire that is automatically shot. So, if you are with 2 charges on Q, and a nearby enemy minion die, you actually earn 2 whitering fires. One is automatically shot, and the other is added to your charges, so you end with 3 charges.

A couple notes about your guide: Lvl 1 talent is for Mercs, not Minions. It's the damage buff of most Merc Lord talents without the damage reduction. Lvl 7 talent Possession is instant kill to minion, plus create your own minion to replace it, vs bonus damage on withering fire only helps to kill and if there is a hero nearby, you can't target the minions anyway. No benefit to hero fighting at all, where Possession can make the enemy very much outnumbered by minions and have to run or let you split push very well by using charges on one lane and moving to another. Lvl 16 talents: I suggest Overwhelming Affliction if you have someone with executioner, and Remorseless for every other occasion. Lvl 20 Fury of the Storm is amazing for either assassin or spec build since it gives bonus damage to main target, plus spreads to all minions/mercs nearby for enough to 1-shot a full minion wave. Combos really well with Possession since you can take over 3, then kill the rest of the wave really fast.

I wouldn't say Mind Control is bad. General behaviour is that the enemy team will try to support the one being controlled instead of trying to kill you

I love this guide! thank you!