In 2001-2002 United (ie the season between Stam departure and Rio's signing) ended up 3rd, 10 points away from Arsenal. Our GA was 45, which placed us 6th behind Chelsea. The season after (we bought Rio), we won the EPL title with a GA of 34 IE 11 less Goals against then the season before. The season after, Rio got suspended (it kickstarted in January 2004) and we ended up 3rd again. That kick started a spending spree which saw us signing Heinze (2004), Vidic and Evra (2006). That's how important our Rio was in his first years with us.
The defense pre Rio and post Stam was shit. Irwin and Blanc were ancient (ancient museum level), Wes and Johnsen were constantly riddled with injuries, Silvestre was hilarious, May was amazingly still a United player and we had the Nevilles. No wonder why SAF decided to invest heavily in the defense in the next years.