Lots of folks rip-off/borrow/pay homage to others. Shakespeare took his plot of "The Comedy of Errors" from Plautus' "The Menachmi Twins". There are some other instances certainly of him adapting stories he had heard as well, which is where I believe "Romeo and Juliet" came from, among others. I'm not familiar with the show "It's a Funny Old World", but it does seem Newley tried to do shows which gave him lots of room to be expansive and cover what seemed to him to be broad themes (and give himself a great star role). It still happens: Damian Chazelle's musical "La La Land" has lots of it borrowed from Jacques Demy's "Umbrellas of Cherbourg" and "Young Girls of Rochefort". Plus tons of musicals have borrowed from the Pygmalion myth and Cinderella fairy tales. The idea of transformation makes for a good musical when done well. Are Chappie and Sir transformed in some way at the end of "Roar of the Greasepaint"? But I do see your point to some extent.