I think that Williams develops the idea that the individual who has strength in the midst of human struggles is representative of the most appropriate response to such conditions. Tom and Amanda initially appear to be the "strongest" people in the drama. Tom is the "man" of the house, while Amanda clearly relishes her role as the chief source of domestic power. Even Jim O'Connor, seen as successful, could be seen as someone with power. Yet, I think that Williams is making clear that each of these individuals lack the capacity to formulate an appropriate response to human struggles. Amanda seems to live in the past. Tom seems to live in dreams. Jim does not seem to be living in much of anywhere that is coherent, as he is uncertain of what he wants. The people perceived as being "powerful" seem the most ill equipped to formulate an effective individual response to human struggles.
I think that that Laura is where Williams rests power at the end of the drama. She represents an appropriate individual response to human struggles. Laura understands what it means to endure. Laura lives in the world of what is and also in what can be, through her love of animals and the glass menagerie. Yet, she does not escape from the reality that surrounds her. Her leg brace and challenges in physical health do not limit her from seeking to bring peace between her brother and her mother. She endures Amanda's constant comparisons to herself in regards to "gentlemen callers." She is left at the end to blow out her own birthday candles while everyone else has reacted inappropriately to human struggle. Laura can be considered to be the strongest character in her responses to what it means to be human. For Williams, I think that Laura becomes the basis of an appropriate response to the struggles in being human.