Don't know about harder to fly, think it is merely what you get used to.
I went through a phase in my career, where I flew the 300/400/500 with periods of only 1 variant for months at a time. After a few days any of them seemed fine, as it was when I alternated between the 3 at once.
In any case, there is much more variation between an empty airframe vs one at Max Landing Mass.
For sure the Classic with its nice thick wing is easier to grease on . . . . but, that is not what we are "supposed" to do anyhow according to Mr Boeing, so, don't complain to him.
FWIW I preferred the 800 pre winglets, but none of them are nicer to fly/land than a 300W.
Oh, and those who have flown the 900 don't have a good word to say about its handling.