This is about as poor a comparison as you could make. As multiple folks have mentioned, passing in the NFL has completely changed since the 1970s and 80s.Not sure why people are saying Plunkett was just as good as Eli....
Plunkett career stats
Completion% 52.5
Pass yards/Attempt: 7.0
TD's - 164 (4.4 per attempt)
INT's - 198 (5.3 per attempt)
QB rating - 67.5
Eli Manning career stats
Completion% 60.3
Pass yards/Attempt: 7.0
TD's - 366 (4.5 per attempt)
INT's - 244 (3.0 per attempt)
QB rating - 84.1
Looking at some stats to compare them with their peers.
Years top 10 Passing Yards: Plunkett 5 (highest 2nd), Eli 7 (highest 4th)
Years top 10 TDs: Plunkett 3 (highest 2nd), Eli 10 (highest 4th)
Years top 10 QB Rating: Plunkett 1(9th), Eli 1(7th)
Years top 10 Interceptions: Plunkett 7(highest 1st - once), Eli 11 (highest 1st - three times)
Years top 10 Completion %: Plunkett 1 (6th), Eli 1 (9th)
Years top 10 Fumbles: Plunkett 0, Eli 4 (highest 2nd)
Years top 10 Sack %: Plunkett 1(9th), Eli 7 (highest 1st)