Wow impressive mileage! The plunger you mention is the hydraulic lash adjuster. The 6.2 valvetrain is somewhat unique in that it has shaft mount rockers with a lash adjuster between the rocker arm and valve tip.
In your case, the lash adjuster failed hydraulically or got stuck, causing excessive clearance between the cam, rocker arm roller, and valve tip. That creates a hammering effect on the cam lobe and roller, because the roller is no longer held against the cam at zero lash as the lobe rotates. The eventual result is the erosion of the cam material visible in your photos.
With the damage to the cam, it will wear on the new rocker arm roller and both will eventually fail. It will also cause metal debris to end up in the cylinder head, which will cause further issues. The cam should definitely be replaced, along with any other damaged rockers. It’s a big job since the timing cover and chains need to be removed, but at that mileage it wouldn’t be a bad idea to replace the chain/guides/tensioners while you’re in there anyway.