Phbbbtt. Nah, not true. (With all due respect, of course!)
I've been with the same man (married and not) for 20 years, since we were both 19, and managed to enjoy it thoroughly. It is less work than dating, that's for sure. Dating inolves gobs and gobs of uncertainty and lack of trust, and the necessity (imaginary necessity, perhaps) of doing painful things like waxing certain body parts that were never meant to be waxed, and the discomfort that comes from lack of true intimacy.
Married (or whatever) is way more fun and enjoyable because you don't have to deal with that kind of nonsense and other kinds of nonsense that people who are dating have to cope with. And it's not work, not really, if you love the other person, it makes everything (including sex) way more fun and less onerous, because you are with someone you love, like and respect.
Maybe instead of "married" I should've typed "in a loving monogamous relationship". That may have made more sense, and it is certainly not work, at least not in my opinion/experience.