Heavy guns move less under recoil. It's simple as that. I don't know of anything heavier then the JP handguard. You can reduce your reciprocating mass more with a Ti or Al bolt carrier and s little less gas too. I run a PRS stock on my guns to help balance the weight out front.
The current fad of running mid length gas 14.5-16" guns for faster transitions is the exact opposite of what you're seeking. I'm still not a fan of that idea. My rifles are heavy.
They voodoo are lower mass but not as light as a standard JP steel carriers or anywhere close to the weight of the Boomfab Titane or the new disposable JP Aluminum carriers. If you want to reduce sight movement in a rifle low mass carrier, buffer and adjustable gas will do way more then a heavy handguard will.
I have a heavy profile fluted 18" barrel, SJC Titan comp up front, and overall a heavy rifle. Right at 12lbs unloaded. I also went with a MagPul PRS, and now a MagPul UBR stock to add weight to the back to balance the gun. I even run a Surefire 6PX light up front. I am running a low mass system with adjustable gas block. When you 1st pick it up, she seems heavy, but once you put it in your shoulder she feels much lighter. Barely even moves when I shoot it.
Weight does help soak up that recoil, but what seemed to make the biggest difference to me was the low mass system, and the comp. I like mine being heavy. Very stable on target, and I am big enough to still be able top swing it fast.
I had the JP low mass buffer and spring when I had the PRS stock on. Now I use the JP silent captured spring with my carbine length UBR. Either will work fine, the silent captured spring is a bit pricey. The silent captured spring also gives you more tunability since it has the optional spring kit with 5 spring weights. I am using the spring that came with it though.