Yes, near misses make top movies better. Big budget movies attract the top names in the business. If there are many actors vying for the same role, this challenge for an important part propels actors to put on their best performance. Actors will work harder in the audition than they would if they were given a part as part of a pre-defined contract. The level of acting will be better, and so will the quality of the movie overall. Great movies are often memorable because of the performances of a few characters - with their unique characteristics and vibrant dialogue. Often actors add parts to the movie that aren't in the original script.
A big name actor isn't necessarily the right person for a specific part simply because of the reputation their name carries. There have been many times in recent history where small time actors were chosen over A-list actors for roles in major films, which resulted in the film doing extremely well as well as the actor gaining recognition and credibility.
The topic of the debate question is unclear therefore I am unable to answer it. It is obviously referring to a certain subject (actors and movies) but the specific content it is referencing are not available. There are thousands of actors in Hollywood and thousands of movies, so unless this topic can be narrowed down, I cannot answer it.
Who did, or didn't get the part is irrelevant. Did the actor who got the part help make it a top movie? That's the only question that counts. If Sean Connery missed out on getting the part of Hans Solo, big effing deal. The only point is Harrison Ford got the role, was great in it, and Star Wars was a great movie. I could have not gotten the part and the movie would have been just as good.