As much as I hate to say it, I think quick tinkering is way too overpowered and needs to be nerfed. I'll explain why I believe this is the case, and also a couple of solutions which would bring the feat back into a more balanced state.
Before I start, I'll preface this by saying I play exclusively hard mode and usually ironman as well. My opinion on this feat is shaped by my experience playing this game on the hardest difficulty with no margin for error. When I die, I restart.
Why is QT OP?
Quick tinkering is the strongest defensive feat in the game. With proper 'technique' you can hold down any single door choke point indefinitely. What makes this feat so powerful is its combination of a 2 turn CD and its synergy with bear traps (to a lesser extent chemical blob traps). QT trivialises combat scenarios where the is any kind of exploitable choke point. The only way enemies can breach your defensive position is if you make a mistake and allow the bear trap to kill its target (opening up the choke point and allowing subsequent enemies to 'breach' you position). When an enemy is trapped in a doorway, you can basically hide behind the corner, wait out the cool down on QT, kill the enemy and then re-lay another trap. The enemies behind will fluff around not doing anything because they cannot walk through the unit blocking the doorway. So you just rinse and repeat indefinatly. As an ironmode player, this feat is the single strongest one in the game.
What can be done to balance QT?
I see two solutions.
Either A, increase the cooldown on QT to 3 turns. The rational being that the cool-down will EXCEED the amount of time an enemy is held by a beartrap (2 turns), therefore requiring a broader strategic approach to a combat scenario. Non more insta-gib.
Or B, Give more enemies Escape Artist. There are NO enemies in the entire game (that I have encountered in numerous playthroughs) who have escpae artist. They ALL just sit there like morons when I trap them. Make them dangerous again by giving some enemies the ability to escape my defensive cheese.
*Edit - There is a third potential solution which is to make QT cost action points. An AP cost would at least make it more challenging to duck back behind a corner in certain scenarios to avoid taking damage. I believe this would be the least effective change however.
In its current state, enemies have no strategic counter-play to QT. As much as QT has made my ironman runs so much more pleasant, it needs to be nerfed!