I'd disagree as in my experience with speed running and I've done 145mph so far you need almost locked diffs. I run 20mil diff oil in my Limitless with a locked center spool. Some of the best in the world will lock the front diff and run 20mil in rear. I'd try to thicken up the diff fluids and play with your front toe. When the diff has light fluids you can have it diff out and cause the spin out as one side is being allowed to spin faster than the other. With locked or almost locked diffs the wheels stay spinning the same speed all the time not allowing the diff out and spin out.
Also I'm sure the lower weight makes it difficult as I tried to run my Tamiya TT01 1/10 and it was a pain and all over. Managed 50mph with it but it's just so light that any little steering correction would cause it to spin and go flipping down the road. That's another suggestion is turn your steering down to almost nothing so when you make an adjustment it hardly makes the car move at all but just a slight turn back to straight. I run my Limitless at 140+mph with my steering at like 7% so adjustments don't send me across or off the road. Here's some attempts I made with the TT01 think I managed 46 or 48mph here but as you'll see it was not easy as I had light diff fluids and steering not turned down enuogh.
And 144 with my Limitless