I'm not sure the fact that JA writes Jane Bennet was happy with Bingley means that he wasn't easily led or "weak".
While a lot of us might think that a woman - Jane Bennet - could not possibly be happy with a Bingley who was easily led or persuaded, it is quite possible that she could, as Jane Austen wrote her. There is no indication that she would look for a man who is a strong-willed independent thinker, a man who makes up his own mind and stands firm to his own decisions. She did look for someone who was kind, friendly, easy to get along with the neighbourhood. A proof of this is that she accepted Bingley immediately after he came back and proposed again. There are many fanfics where Jane doesn't accept him right away, or not at all, because she is afraid that he will be again weak at some crisis or not constant to her or influenced by others - expressing the belief of many of JA fans that this is the better decision.
For another example, to this day, I can never truly believe that Charlotte Lucas could really be content in the long run with Mr. Collins and that it was a truly good decision to marry him, although I have learned to appreciate her motives and her ability to be content in this marriage as much as possible. I can imagine the same is true for Jane Bennet (if I choose to view Bingley in the worst light) - she can be happy where I might not be.
As for Elizabeth and Darcy respecting Bingley, I'm sure they did not think he was a "wishy-washy wimp" but towards the ending, after the reconciliation with Darcy, Elizabeth has some less than respectful thoughts about how Bingley could still be influenced by Darcy - which she keeps to herself because she doesn't feel Darcy would be comfortable with her teasing. him about it.
