English is not more difficult to learn than any other language.
The last one ("pop", and mother with "mop") didn't make any sense to me, but the rest was funny.
And yet, despite what the native-speakers like to believe, English is a ridiculously easy language to learn relatively to just about any other... Go figure.
"Father" and "Pop" share absolutely no linguistic heritage (and have none of the same letters, actually). "Pop" is a morph of "papa," which comes from French and ultimately Latin. "Father" comes from Old English "fæder" and ultimately Old High German "fater." This actually illustrates English's dual heritage, borrowing much from Latin through French to supplement its own German lineage. Anyway, "father" yields nothing in "pop," so why would we replace the first p with an m to form "mop" for a shorting of "mother"?
This picture lies a lot. And isn't even about the language really.