I always aim to replace my unloaded steer weight and get the tongue weight down to 12.0 percent for TTs. This is comfortably enough tongue weight to keep even flat front TTs from swaying at 65 mph. Steer weight is mostly about getting it in the zone so to speak. If you are 100 over or 100 under the unloaded steer weight its not likely to make the difference especially if tongue weight percentage is good. Now 4-500 pounds under with no weight distribution yea that's probably sketchy to drive, easy to roll, hard to stop.
I Like to see this type thread showing setup and adjustments according to scale results. As well as the Mfgr spec numbers to determine within spec or not and for setting up a safe stable tow. Instead of the ad-nauseum "advice" stacking of weight guesstimates towards a payload sticker number that while commonly being the first spec exceeded in itself is hardly a significant indicator of what a properly set up tow vehicle can handle.
Regardless of whether you are slightly above or below where you want to be with steer and tongue weight you will know you have it right when its stable in wind gusts or when a fast close passing semi bow wave doesn't wiggle your trailer & truck like some kind of white knuckle accordion ride. But rather just pushes you away a bit with your truck and trailer feeling almost as one solid unit. It should generally be two fingers driveable and not require two hands at 10 & 2 at all times.
Mfgr max specs such as axle weight, receiver weight, CVW combined vehicle weight and GVW gross vehicle weight also important to review but achieving an optimum or in the zone stability is found in the steer & tongue weight.
785,000 miles towing TTs for the Mfgrs over the last 7 years thats a pretty decent distillation of what I have learned about setup & stability. Great thread.