You're not on pavement....... IF you plant the tires on a pulling track as hard as you would on pavement, you're not going to go very far.............. Unless the truck has the power and traction to drag the boat from a stand still with the weightbox at the end fully on the pan.
At the begining you should very well be able to plant and move since the weight is at the back, i would want to plant and get it moving as quickly as possible before relying on wheel speed
It doesn't hinder anything. Nothing is slipping along. The front is pulling if you spin the front faster then the rear it applies more force to the front tires which helps take some of the load off the rear. This isnt that hard to understand and your making it way harder then it needs to be. I am getting the idea you don't know much about dirt stuff. Look at a dirt sprint car. Different size tires on the same axle. Bet that doesn't work either does it! Bigger tire on the outside to make the car turn. Its moving faster to pull the car around. Same theory only we are using faster gear or bigger tire to pull the front faster then the rear.
Actually that is done because you don't want drag, you want it to roll free or we can call it bind, so the outside tire goes around the long way and covers more ground so that stagger is done purposely to remove all possibility of drag, the axle is locked there is no diff, like a pt case, if one end is faster then the other but not covering the same ground differently it's drag or bind, don't want that in a turn it creates slow.
You also run a heavier spring on the inside to keep that tire planted and weight jack. I don't and have not seen any type of countering the effects of the sled and transfer the weight
Now since you aren't turning and the front of the truck isn't doing anything different than the back other than being unloaded i can't see how forcing a unequal transfer on the same frame is helping.
The way i see it, you want to definitely try and plant it off the start and get it moving without wheel spin when it's at it's lightest.
Also saying 4.11 and 4.10 is the same as 4.9 and 4.5 is way way off
A factory truck with 4.11 and 4.10 is due to which way the teeth are designed to be the quietest and packaging of it in that diff , but that .01 isn't ANYTHING like .5 to .9 but also you have never ever seen a factory truck come with 4.9 rear and 4.5 front or 4.5 rear and 4.9 front, that just won't work at all.
To show how bad bind is, take a pt case which most of us have and we have 4.1 to 4.1 and go in the street and just turn the wheel full lock, remove your foot from the brake and see what happens.
Do the same in dirt
Hit the gas in both cases on both surfaces, dirt is more forgiving, but the bind and power being used to overcome are still there.
So if you had a 35" tire at both ends and aired down to 10 lbs so you can increase your area, you then could rely on power and gearing to get you up to speed quickly while the weight is off.
So as you go down the track and the weight is added and the drag becomes harder, now the truck is having to overcome that and the odd gearing it has front to back as that pressure is increased, you don't feel it because the wheels have no traction, but there is a drag present.
The same way you have power being lost due to just a simple design, there is a power consumption there.