I find Enid Blyton quite fascinating. Because although people accuse her of sexism-when she wrote them she was actually the other way.
To have George doing what the boys did-and better that them was really not done at the time, probably caused a few raised eyebrows. Not having the girls staying at home keeping out of danger was probably considered by some people that the boys had failed to keep them safe.
And I loved Anne when I read it, the descriptions of her "housekeeping" the cave in Five Run Away Together had me so jealous. I wanted a cave to do that to! Anne is actually written as a very brave character. She doesn't enjoy the adventures like the others, but she's not going to be left out and does her bit too.
I would definitely have been Anne. Dick to me has the least character.
But interestingly, if you read Russell Davis (?) account of filming the FF in the 70s, he wanted to be Dick from the start.
Her characters have similarities-as do, I think pretty much all authors who write a lot. Noel Streatfield, for example, tended to have a small rather pretty, slightly spoilt one, often good at dance (Louise, Lydia, Posy, Holly ...), a not-considered-pretty rather awkward one (Vicky, Gemma, Petrova, Jane,the boy in curtain up...), and a responsible (but talented) older one (Isabelle, Anne, Pauline, Sorrel...).
But I don't think all her groups are clones.
Famous Five: Leader (Julian), Tomboy (George) Second (Dick), Younger sister content in who she is(Anne)
Five find outers: Leader, show off and arogant (Fatty) Second (Larry), Pip (irritating big brother) Daisy (responsible, slightly mothering) Bets (youngest, trying to keep up with the older ones)
Adventure series: Neither Philip or Jack totally take the lead. Philip is the animal lover somewhat impetuous and inclined to a temper, and Jack is calmer, and a bird lover. Dinah, not a tomboy, but determined not to be left out. Lucy Anne, nervous, happy to follow Jack anywhere, even into danger, but not wanting adventures for the sake of it.
Adventurous 4: Andy is the leader, having left school to be a fisherman like his dad. Tom, not too disimilar to Dick as in second in command, but never jostling for leadership, tends to carelessness. Mary and Jill are identical twins, but Jill is definitely the leader and more inclined to have ideas etc.
I think if EB had written a story with a mix of these characters in, but not saying which they were, then you'd probably have been able to pick out which one they were. You can see similarities, but there not identical. And the form in which they're written means that similarities are inevitable. Just thinking about it Julian and Dick are in a lot of ways younger versions of the Hardy Boys with Julian as Frank and Dick as Jo.