Just thinking out loud... 
For serious rock crawling, a very heavy vehicle is going to be more susceptible to damage and breakage. I’ve seen heavy vehicles attempting to negotiate a rock crawling trail, they struggle and too frequently break down.
A vehicle set up for overlanding and long term boondocking is typically set up with extra survival and comfort equipment, adding lots of extra weight. But typically, those vehicles do not do serious rock crawling.
I understand why someone might want to build a purpose-equipped bigger and heavier vehicle that can do serious rock crawling, but overcoming gravity, high center of gravity, and the power requirement is going to stress the braking system, chassis, suspension, drivetrain, and engine.
A 1999 4Runner is nearly 1,000 lbs. heavier than a 1999 Tacoma. Half a ton is a lot of weight to be moving over big rocks.
Likewise, moving heavy vehicles over sand or mud also takes more horsepower, higher strength suspension and drivetrain.
It’s obviously a challenge to build a large heavier vehicle that is capable of trail running over big rocks and maintains a reasonable level of safety and reliability.
As I said before, I admire those that can do it… I could not. 
Gnarls. 
The wheeling here in HI is way different from how the upper 49 states have. I’m from Oahu and our wheeling is more ruts and
. Hill climbs and bouncing off tree is how we wheel here. The other islands, like Maui has a lot of Rock trails like the mainland. Mud, ruts, hills and trees is how Oahu does it. The truck that I built in WA was built with the intention of exploring. It did us good for 14 years. I did the SAS in October 2021 when my Wife said we were moving back home. I wheeled it 2 years since being back and I still have all my
in the truck what’s making it heavy. Now that I just installed the 5 speed, the weight will follow.
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