Context is always going to matter, and that applies both ways. People who point to Roethlisberger as a winner in his rookie season like to ignore context as well (as you point out). The reality of that Steelers team is that they were just a team in need of a QB who wouldn't wet himself. In 2001, they won 13 games with Cordell Stewart as the QB. In 2002, Tommy Maddox took over, and the next two seasons were 10 wins and 6 wins. The 10 win season got them Polamalu and Ike Taylor, which would pay off handsomely. The defense went from 16th in 2002, to 15th in 2003, to 1st once Troy had a season under his belt. So Big Ben's rookie year is an excellent story, and an excellent data point, but it's not anything definitive.
But whether posters like it or not, and fully acknowledging that exceptions exist, rookie QBs drafted in the first round tend to play like rookie QBs, not like quality NFL QBs. And we all know it around here, because we see how BB tortures them when he plays against them. But that gets ignored when there's an agenda involved.
So let's hope that Jones, who's been extraordinarily well prepared and looks to be highly advanced in areas critical to the success of a QB in a Patriots style system, is an exception.