Your observation 'Lady Catherine who had control over all things great and small, in the end, could not control Darcy and Lizzy making null and void one of greater desires' appears true. Charecters like Wickham and Lizzy attest to Lady Catherine's authoritive air and self-importance yet she does not seem a formidable charecter. In Lady Catherine's last scene in the book, Lizzy refuses her the relief that she and Darcy are not engaged, even though she doesn't expect him to propose again. Lizzy simply knows it is improper for Lady C. to ask her such a personal question. Apart from Mr Collins and daughter Anne she doesn't appear to influence anyone, certainly not Lizzy nor Darcy.