Ron ... sometimes "tradeoffs" are a bias in the mind of the designer or marketing person. They're not always "really necessary" tradeoffs. The Tiger's (about the same size rig) tanks are a bit larger, for instance.
You've probably been down under your E350 many times, as I have our E450. There's a whole bunch of open space up high against the coach floor in between the driveshaft and the two main lengthwise truck frame members. Long, flat, large grey and black tanks could be mounted up there - with skid plates and tank heaters on their bottoms - and with on outlet on each end to counter their long length along the axis of the motorhome when parked/camped on lengthwise grades. Some time ago I read of a Class C owner who added a 150 gallon freshwater tank up underneath their RV - for warm weather beach camping use (probably no skid plates or tank heaters, though). I mounted an additional 40 gallon gas tank up under against the frame of a Dodge van camper this way once - that the DW and myself had converted into a van camper in which we wanted a 1000+ mile cruising range.
For additional fresh water capacity inside a Class C's warmer environment, there's most likely several unused voids in behind cabinets where one or more 5-15 gallon fresh water tanks could be plumbed in to feed the main fresh water tank. Our Class C has some hidden open voids inside like that.
All it takes is a can-do attitude on the RV builder's part combined with aware enough and demanding enough buyers to at least offer larger tanks as an extra cost option. I would have paid for larger tanks if we'd had a choice ... there is physical room for them in and around our Class C.
Of course options like this would require that the chassis used under the coach have the additional weight carrying capacity to deal with the larger tanks.