Speaking as a pilot it is often more or less impossible to achieve a CDA with uniform descent rates within the margin of or above 1000fpm as the aircraft simply won't slow down. A heavy 320 with Sharklets and a tailwind bears that out perfectly. Therefore you almost always need to get under the nominal glide path then slacken off the rate of descent to achieve the deceleration.
I agree hammering it down then reducing to 200fpm is a bit much though but what doesn't help is that Gatwick Director is almost always over optimistic with the estimated track miles, especially on 08. That is not a criticism as such as I appreciate it will often be very difficult to be that precise. However it does ruin the execution somewhat if you're told 21 miles by Director and it ends up closer to 30.