After drafting Eli and trading for Rivers, Brees came into his own. Whether it was just natural growth or the drafting of Rivers lit a fire under him is unknown. But he was very good in 2004 and the chargers went from 4-12 to 12-4 and hosted a first round playoff game which they lost in Marty fashion, by going ultra conservative and the kicker (who they got in the Eli trade) missed a 40 yarder in OT.
In 2005 Brees was franchis tagged to his dismay as he wanted a guarantee, regressed a bit but was still good, but in the meaningless season finale he got his shoulder bashed in trying to recover a fumble in his own endzone. Doctors told the chargers he had little chance to come back from it. The chargers had Rivers waiting in the wings, offered Brees a contract that Brees found insulting and was still upset that he was franchised for this very reason sought other offers. 2 teams offered him a contract. The dolphins who offered him the same the chargers did, an incentive laden contract and the saints who desperate for a QB offered him a lot of guaranteed money. He chose the guaranteed money and the rest is history.
Who cares... Eli did good by not giving the press fodder where there did not need to be any....
It probably didn't cost the Giants any other super bowls and theres no telling if Rivers even would have won any if he were a giant (and according to Accorsi he wouldn't have even been a giant anyway as he wanted Big Ben). So Giants fans have a right to be happy with how the trade worked out regardless of who the better QB is, was or turns out to be.