[labrador]

Your title says "Is it possible for someone to not be cut out for software engineering?" while your first point says "Does there ever come a point where it just isn't worth it to continue trying to be a software engineer who can get into top-tier companies / projects?" which are two very different questions.

It'd be like me asking "Is it possible for someone to not be cut out for jogging" and then changing it up to "Does there ever come a point where it just isn't worth it to continue trying to be a runner who can win the Boston Marathon?"

Most of us programmers can't get hired at Google because we don't have the pedigree, the work ethic and other qualities it takes to be at the top of the game. That doesn't mean we don't enjoy and make a living at computer programming.