A person who goes into a potential armed encounter with his body armor in the trunk does not have an "extraordinary mindset".
I agree that once he got into the fight he did very well and his mindset DURING the fight leaves nothing to be desired. But clearly he didn't go into the fight with the proper preparation and that makes it obvious that his mindset was less than ideal going into the fight.
I think body armor in the trunk is more a tactic. However, it would be tough to seperate mindset from tactics, so I won't try.
I'm just trying to point out that most officers go on the job with similar "mindsets"--attitude would be a better description.
When the Monte Carlo was spotted and the agents were notified, I suspect all of their mindsets changed in a hurry to "this is the day".
What didn't change for Mereles, is that his vest (that wouldn't have stopped .223 rds.) was still in the trunk of the car where he couldn't reach it and he couldn't do a dang thing about it at that point.
Poor tactic/mindset re: his vest? OK, but not so bad having his shotgun handy. The only long gun on the good guys side.