Lats and traps grow (more so if a shrug or semi hi-pull is included at the top of each rep) because of the stretch/pull of the exercise. The bar is only being held in position, with most forms of the DL. Which may suggest the value of the static hold for increasing strength and size.
With the Romanian Dl (where the back is flat, lower back set and a slight break at the knees), it allows a limited forward bend of around 90 degrees, very serious weight can be worked up to. Lot of power guy's set the rack pins/or boxes for the bar rather than a hang grip type movement. With this short ROM, most BB'ers could get to 400 plus without that much problem. 500's plus is not out of the question for some who work with serious intent. The GoodMorning exercise is another great movement , in the class of the Romanian & SLDL. Any one of these should increase the squatting abilities very well indeed.
The SLDL requires more of a rounded position of the back. Actually most BB'ers who think they are doing a proper regular DL, are actually doing a partial SLDL, if they would look at a video of themselves working out. A too rounded back puts undo pressure on the small of the back. I prefer the Romanian DL, just a personal choice. Though have used the SLDL, heavily in the past.
If doing either Romanian, SLDL or GoodMorings for the ham stretch, than suggested that the toes be put on a 2X4, pair of 45's, set books, etc for a much better stretch on the hams and the calves. Lighter weights advised, not meant for truly heavy lifting. Good Luck.