The above perks already sited, one needn't look far to see the successes of Steinlager II, as well as the Dashew's boats. There were, of course a LOT of other very successful ketch rigged ocean racers in that era. And the Dashew's, as well as Brion Toss, devote a lot of text to espousing ketches.
Upwind vs. the same boat, but sloop rigged, you'll lose a bit. But fall off some, & a ketch with decent sails is a nicer ride.
Lower center of effort, less stresses on the hull
, & sails. Easier to fly more, & smaller (easier to handle sails).
I think they kind of fell out of favor, when the materials & tech made it easy to build monstrously sized sloop rigs. Which, when coupled with a good hull
& foils design, and a rock star crew... well, naughty's faster. Not even something with "unlimited" power, a US Navy
submarine with it's own nuclear power plant... up to & including in a circumnavigation