I think it is the diminutives that reflect the personality. Take Robert for example. Bert = a big burly chap; Rab = a tough one; Bobby or Bertie is a bit soft, a mammies boy, whereas Bob is a fun guy.
Take Margaret. Some remain as Margaret, but most grow up to be Maggie, Mags, Rita, Meg, to suit their personality. The same can be said of the thousands of Elizabeths - Liz, Lizzy, Lisa/Liza, Beth, now Lilibet!
My father never called me by my given name. As I was small he always called me Toots and on formal occasions referred to me as Daughter No2!