It's absolutely true. I used to drive my 6,000 lb squarebody all over the Oregon sand dunes in 2wd because it had big, wide tires that I'd drop down to 10 PSI. This had a stock small block V8 that probably put out a whopping 150HP.
Just tire pressure alone can make or break even the most capable vehicle. You need to float on the surface, not dig in. Street tire pressure will make your vehicle dig in and get stuck immediately regardless of weight or horsepower.