I enjoy dr-t but as you say it is far too easy for max level players. I usually do stages 1-6 with one boat of zookas and Bullit, often without reloading. Stage 7 is trickier so two boats although I have gone four boats a few times. I treat it as a puzzle, I guess the whole game is a puzzle really.
Prototypes would shake things up.
It is also a great thing for practicing landings, Bullit shocks, smoking etc and just good practices in general but it needs more demanding stages after 7 even if the rewards are limited in some way.
As with a lot of things in Boom Beach, the bones are good but it needs fleshing out.