I doubt there is any significant weight difference at the rear for a rear kitchen model. Would be interesting to see some data to substantiate that. With our rear kitchen (29' length), the tongue weight is almost 15 percent.
We absolutely love our rear kitchen. It has way more counter space and makes for an efficient use of floor space. I agree with adding shocks. We used to get a lot of bounce that would not only open cabinet doors but would also throw the grate off the stove and even the vertical plastic rod for opening & closing the blinds would jump off the hook. Stopped to get groceries once and found coffee all over the floor because the pantry door flew open.
If looking at a RK model, I would avoid one that has a frame with fabricated 3-piece I-beams because they flex a lot more than a one-piece type and cause more bounce in the rear.
The amount of bounce at the rear will depend on the length of the trailer, GVWR, spring rating, frame design, axle location. We added shocks and now our trailer rides like a flat line down the road. No more stuff bouncing around. Adding shocks has other benefits too is a good upgrade regardless.
If there is a downside to a rear kitchen, is that you can only have a small window due to the upper cabinets. Used to have a TT with a huge picture window at the rear and I really miss it.