When The Falcon and the Winter Soldier first came out, I was really looking forward to it. I won’t say I was disappointed after watching it, but I will say it had a few week spots. Well….it had one MAJOR weak spot: I didn’t really buy the Flag Smashers. The concept was great, but the execution was a bit off.
The one thing I thought it did brilliantly, was John Walker. His storyline perfectly summed up the problems with trying replace Steve Rogers, and why Sam Wilson was so reluctant to assume the mantle of Captain America.

I thought the character was far more tragic than villainous. He was a well decorated soldier, and as such probably figured he could handle anything the role of Captain America could throw at him, but I think the reason he didn’t work out at well as “The Captain” was because he WAS a veteran soldier.
During the entire Infinity Saga they always referred to Cap as “The Soldier”, but all we really saw of his time in the military was his time at basic training. Immediately after basic he volunteered for the Super Soldier Program, then did the tour raising war bonds. After saving Bucky and the 107th, he was given his own unit, so he never really spent any time moving through the ranks, dealing with superior officers, and (basically) having his independence removed. He became his own version of a perfect soldier, and not the military’s version.
His real super power was his morality. Which he was able to keep due to the limited influence the military. After his long career in the military John Walker did NOT have Steve Rogers morality, and that was why he couldn’t be a good Captain America.
It was implied that John Walker had a successful and distinguished military career, and as a veteran soldier violence is always gonna be on his list of solutions to a problem, probably rather high up on that list. With Steve, I always felt he used violence as a last resort.
Lets look at the elevator scenes. The scene in Winter Soldier is a brilliant scene, Steve started in the elevator and the STRIKE Team came in looking for a fight. Which was amazing!! In Endgame the STRIKE Team was in the elevator and Cap came in. The audience (at least I) expected another awesome fight scene, but Cap used subterfuge to achieve his goal. Somehow, in that situation, I don’t expect John Walker would have used the subterfuge.
That is the essence of why John Walker failed as Captain America.
Which is also why I felt so bad for the guy. He was so honoured to be chosen as Steve’s replacement, and I think he really, truly tried. Sadly, he made all the wrong decisions because of who he was, and not because of anything he had any real control over.