I would never, never accuse King of overreaching. No one who creates a successful mystery series with a 20-something wife for Sherlock Holmes is overreaching. However, in this volume in the series, the apt word is "misapplied".
Fflyttes of Fancy - just saying that phrase again makes me wince. It's as if King thought of a really good set of puns and decided to build a story around them. A ridiculous story with "real" pirates set against the "fictional" universe of Pirates of Penzance, drifting from England to Portugal to Morocco and thankfully not back again (although England would have been a welcome respite to the more "exotic" locations described). Also, it's as if she wasn't re-reading her own story, because she tells us over and over in the beginning why the actresses have been given names other their own. By the third time, I was feeling decidedly alarmed about the rest of the book.
And, yes, Mr. Pessoa may, in fact, have been a real person, but I could not have cared less about his peculiar personal outlook on life and his own "flights of fancy". In fact, that really sums up the entire novel for me - I just didn't care. The more ludicrous it became, the more offputting it was to finish.
I notice that it does get some of the lower reviews on Goodreads than her other novels, and that the next one has a slightly better average rating, so here's hoping.