As long as your dot is fast enough, returns are about:
1) The blockers
2) Not fumbling
3) Breaking tackles
Carrying is the primary attribute for both #2 and #3 and there's nothing as a returner you can do about #1. Agility needs to be up there to get your Spin on, but you don't need me to tell you Speed/Agi are important. Strength is less important than Carrying for breaking tackles, and waaaaay less important for fumble protection.
At the Pro level, you're going to get hit by a player with 15% to all attributes (spec teamer VA), +45% fumble forcing (power tackler VA), another +25% fumble forcing (AEQ) and probably a bunch of Big/Monster Hit SAs almost every return. Sure, you can counter with your own AEQ/VAs, but the Return Man fumble protection bonus is smaller than the Power Tackler bonus to fumble forcing. And even if they were exactly the same, ask yourself what it would take to win a straight up tackle vs carrying comparison.