Can we say that history is the proof that Peyton Manning, Eli Manning, J Allen, and Roethlisberger all benefited from starting their rookie year?
There is no right and wrong. Some QBs sat and some QBs played. Some QBS that sat worked out but others that sat were YAGs. Some QBs that played their rookie year worked out and others that played their rookie year were YAGs. There is no historical right or wrong.
I would argue Peyton Manning led the league in INT's specifically because he was put on a horrible offense and was forced into a trial by fire. He late had a huge INT problem compared to other elite QB's in his era that followed him throughout his career. In big games in the playoffs, that would manifest when he felt pressure and did him a huge disservice. Eli didn't start until late November. The team was 5-5 and finished 6-10 so you could argue they jumped the gun on making a move when Kurt Warner had a two game losing streak and then blew any real chance at the playoffs. Then let's be real, Eli was not some elite QB. He was a streaky QB that got hot at the right time twice. But the dude was very middle of the road otherwise and was not ideal to build around. Allen didn't really come into his own until year 3 when they gave him a binky. Even then we could split hairs on whether the first two years helped him or gave him some bad habits that led to him having some real stinkers. It's sort of in the we will never know category.
Ben I would agree with, but Ben was a different animal. He could extend plays early on which mitigated one of the biggest fears teams have in throwing out a new QB too fast. You didn't have to worry about him being under the same pressure and timer. He also already had great footwork so you could feel confidant there.