Phil Simms also led the Giants to two super bowls, and he did it with lesser WRs and a lesser O-line. Simms got sacked like crazy during his tenure, but still was consistent as hell and passed with incredible accuracy. Manning has been less consistent and he is surrounded by better talent.
We will be better able to answer the question once Manning hangs up his cleats.
(And incidentally the 18-0 Cheatriots were over-rated.)