I have a soft spot for Mary, she’s not clever or beautiful and she gets a bum deal.
Same here - the only way she could compete with her pretty. clever, witty sisters was - not to compete! Instead she became a parody of herself - she was considered plain and dull, and became ferociously so without being aware of it. I think she was desperately lonely and unhappy - her two older (gorgeous) sisters were in each other's pockets; her two younger (flighty) sisters were inseparable - all she had left was to try to be clever, but sadly wasn't particularly bright.
Maybe the Bennets should have directed Mr Collins to her, but she wouldn't have suited him, because she wouldn't flatter his ego.
I think when her older sisters get married, and Catherine snags herself a soldier (as she surely will if Mrs Bennet gets her way) or an apothecary (if Mr Bennet can keep her under control), Mary may have a chance to become herself.
I like to think that when she stops being so fiercely competitive with her sisters, she will accept that she is a pleasant though nor very bright young woman, and marry a local draper ("Mmm - that's a nice bit of muslin, Miss Mary . . . ") and turn out to have practical skills as a Milliner to the Stars. It will be a step down for her socially - her father is a gentleman, and her husband would be in trade - but she would probably be happy to find someone who listened to her ramblings, and to get rightful praise for her hats and bonnets.