The point you continue to miss is that foreshadowed or not, the Thor/Thanos final scene was poor screenwriting when Thor has participated in battles where putting an absolute end to enemies was the goal.
This is all wiped away by Thor fully comprehending the threat of Thanos using the gauntlet if he successfully found every stone. That was a repeated point in the film for every sub-group, with Thor realizing it more than all others, with the exception of Dr. Strange, so again--and above all else--the film sets up Thor needing to kill Thanos on first strike, not go far enough that Thanos has even a moment of life left in him.
It would be fatal...to an ordinary person. The films have built Thanos to be more than Joe Average male life form who is easy to kill. Moreover, with Thanos wearing the bejeweled gauntlet (and the repeated build up of that threat throughout the film), there's no excuse for Thor to underestimate Thanos and do anything less than driving that axe through Thanos' head...other than to have him be the thinly plotted screw-up who allows Avengers 4 to happen.
In this case--as in the battle of New York--Thor did not need leadership to end the threat. That was the character's drive right up to the ridiculous halfassing of his strike. I do not doubt that if Captain America, Wanda, Black Panther, Bucky or Okoye had the ability to "take the shot" at killing Thanos with one blow, they would have, and made sure their first strike was also the last. One does not need to act as part of a team to understand the magnitude of that mission.
