Right... up until the calculation of what it does to the enemy.
Spells get a weapon rating equal to their power, and the control roll doubles as the attack roll. So, in your example, the attack goes off at fair (+2), that being his control result, and exactly hits - 0 stress from accuracy. But it's a weapon 5 attack, so that's a 5 stress hit, and the enemy has to take a moderate consequence (something like, say "cuts all over") - and still has to mark off his first stress box. For a mook level opponent, this'd probably go straight into concession territory; perhaps he gets knocked out by the attack; perhaps he takes his moderate consequence and flees in terror; up to standard concession negotiation (and what the GM wants to offer).
By contrast, if the enemy had rolled a mere +1, he'd have dodged the attack entirely - no hit, no consequence, no stress.
Follow up question: Correct. Or the wizard could pass that free tag to one of his allies if he wanted to - but that's up to the wizard's player.