Not quite. The to hit formula looks like this:

Chance to Hit % = 100 x __AR / (AR + DR)__ x 2 x Alvl / (Alvl + Dlvl)

AR= attacker's attack rating, DR = defender's defense rating, Alvl = attacker's level, Dlvl = defender's level.

ITD sets the defender's DR to 0, so the underlined part becomes 1, turning the formula into into this:

Chance to Hit % = 100 x 2 x Alvl / (Alvl + Dlvl)

That means if your level is at least the enemy's level, the formula provides a 100% chance. However, the chance has an upper cap of 95%. The highest level of regular monsters is 85 which means that ITD works at its optimum from L77 on.

Bosses and players are immune to ITD. For that purpose, -x% target defense is better, as it works at half strength versus them.

ITD and -x% target defense have no effect on blocking and the dodge/avoid/evade skills from amazons.