Your average off-the-rack suit coat has to accommodate many different potential body shapes. Some people have wrists with a diameter greater than two inches. I wish these people nothing but the best. However, they lead to the problem pictured above. Call it Sleeve Gap.
It is a fairly straightforward alteration to have done and should be done on all suits. The question is by exactly how much to reduce the volume. I say give yourself about half an inch, tops, from the tip of your French cuff to the inside of the sleeve. That should leave enough room for sliding while solving the problem of flopping.
This suit has been fixed since I took this photo, and the result is delightful.