No.
The Colts had the first pick of that draft and they chose Manning.
There was great debate between the 2 QB's on whom was better and were projected by many "experts" to go 1-2. With Manning gone the Chargers selected Leaf, it just didn't go the way they planned it.
There are several other worst choices out there over the years (look at anyone's top 10 draft flops off all time) but they don't get the attention that Leaf does because the other choice didn't have a career as stellar as Manning's.
Now if the Chargers had the #1 overall pick and selected Leaf over Manning and seeing how everything turned out I would say yes. But then who's to say that Leaf wouldn't have flourished as a Colt while Manning floundered as a Charger? I guess we'll never know.