Yeah, that much vertical offset isn't good. A collision would likely cause the towed vehicle to climb on top of the tow bar and take up residency inside the rear of the motorhome. I wouldn't be too concerned about the extra length. IMO, it's more important to get the towbar leveled to within spec. We tow one of two vehicles - an Acura MDX, which uses a 6" riser, or a Jeep Rubicon with modified suspension and 35" tires, and it needs an 8" riser.
We use the same Blue Ox tow bar for both vehicles. When towing the Acura, its side of the tow bar is about an inch lower than the MH side, and it's always rock solid behind the RV. The Jeep side of the towbar, however, was originally about two inches higher than the MH side, even with a 6" riser. That's within the 3" spec for the towbar, but even so, the Jeep tended to wobble a bit behind the RV.
Because of that, I replaced the 6" riser with an 8" riser, and I also installed some hitch clamps to tighten the whole hitch assembly up. That leveled the towbar and solved the wobbling issue. I think the wobbling issue was probably caused (in part) by the modified suspension and oversize tires on a short wheelbase vehicle, but who knows.
Kev