TwoSix
Everyone's literal second-favorite poster
Your issue is that you're looking for a reason for it to NOT work than a reason for it TO work.So your position is that its reasonable for my fighter to be able to ToI every round stabbing the same enemy over and over knocking him 15 feet away and prone with no opening. Yet to stand still and stab someone twice requires an opening that can only occur once per encounter? If you don't see an issue here I'm not really sure what more I can say to enlighten you.
D&D doesn't make sense. It's never made sense. Every part of it breaks down if you look at it too hard.
Decide what kind of game you want to play, and pick your edition. It's not hard. I just want 5e to support the kind of game I want to play. Ideally, that would be a module with support for even more narrative aspects than 4e did.